Function vcpu_is_preempted() is used to check whether vCPU is preempted
or not. Here add implementation with vcpu_is_preempted() when option
CONFIG_PARAVIRT is enabled.
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
arch/loongarch/include/asm/smp.h | 1 +
arch/loongarch/include/asm/spinlock.h | 5 +++++
arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
arch/loongarch/kernel/smp.c | 6 ++++++
4 files changed, 28 insertions(+)
diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
index 3a47f52959a8..5b37f7bf2060 100644
--- a/arch/loongarch/include/asm/smp.h
+++ b/arch/loongarch/include/asm/smp.h
@@ -18,6 +18,7 @@ struct smp_ops {
void (*init_ipi)(void);
void (*send_ipi_single)(int cpu, unsigned int action);
void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
+ bool (*vcpu_is_preempted)(int cpu);
};
extern struct smp_ops mp_ops;
diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
index 7cb3476999be..c001cef893aa 100644
--- a/arch/loongarch/include/asm/spinlock.h
+++ b/arch/loongarch/include/asm/spinlock.h
@@ -5,6 +5,11 @@
#ifndef _ASM_SPINLOCK_H
#define _ASM_SPINLOCK_H
+#ifdef CONFIG_PARAVIRT
+#define vcpu_is_preempted vcpu_is_preempted
+bool vcpu_is_preempted(int cpu);
+#endif
+
#include <asm/processor.h>
#include <asm/qspinlock.h>
#include <asm/qrwlock.h>
diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
index b1b51f920b23..b99404b6b13f 100644
--- a/arch/loongarch/kernel/paravirt.c
+++ b/arch/loongarch/kernel/paravirt.c
@@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
#ifdef CONFIG_SMP
static struct smp_ops native_ops;
+static bool pv_vcpu_is_preempted(int cpu)
+{
+ struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
+
+ return !!(src->preempted & KVM_VCPU_PREEMPTED);
+}
+
static void pv_send_ipi_single(int cpu, unsigned int action)
{
int min, old;
@@ -308,6 +315,9 @@ int __init pv_time_init(void)
pr_err("Failed to install cpu hotplug callbacks\n");
return r;
}
+
+ if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
+ mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
#endif
static_call_update(pv_steal_clock, paravt_steal_clock);
@@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
return 0;
}
+
+bool notrace vcpu_is_preempted(int cpu)
+{
+ return mp_ops.vcpu_is_preempted(cpu);
+}
+EXPORT_SYMBOL(vcpu_is_preempted);
diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
index 46036d98da75..f04192fedf8d 100644
--- a/arch/loongarch/kernel/smp.c
+++ b/arch/loongarch/kernel/smp.c
@@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
panic("IPI IRQ request failed\n");
}
+static bool loongson_vcpu_is_preempted(int cpu)
+{
+ return false;
+}
+
struct smp_ops mp_ops = {
.init_ipi = loongson_init_ipi,
.send_ipi_single = loongson_send_ipi_single,
.send_ipi_mask = loongson_send_ipi_mask,
+ .vcpu_is_preempted = loongson_vcpu_is_preempted,
};
static void __init fdt_smp_setup(void)
--
2.39.3Hi Bibo,
kernel test robot noticed the following build errors:
[auto build test ERROR on 6a23ae0a96a600d1d12557add110e0bb6e32730c]
url: https://github.com/intel-lab-lkp/linux/commits/Bibo-Mao/LoongArch-KVM-Add-preempt-hint-feature-in-hypervisor-side/20251118-161212
base: 6a23ae0a96a600d1d12557add110e0bb6e32730c
patch link: https://lore.kernel.org/r/20251118080656.2012805-3-maobibo%40loongson.cn
patch subject: [PATCH 2/3] LoongArch: Add paravirt support with vcpu_is_preempted()
config: loongarch-randconfig-r052-20251120 (https://download.01.org/0day-ci/archive/20251120/202511201009.WLpYNMAM-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251120/202511201009.WLpYNMAM-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511201009.WLpYNMAM-lkp@intel.com/
All errors (new ones prefixed by >>):
>> arch/loongarch/kernel/paravirt.c:346:14: error: redefinition of 'vcpu_is_preempted'
346 | bool notrace vcpu_is_preempted(int cpu)
| ^
include/linux/sched.h:2263:20: note: previous definition is here
2263 | static inline bool vcpu_is_preempted(int cpu)
| ^
>> arch/loongarch/kernel/paravirt.c:348:9: error: use of undeclared identifier 'mp_ops'
348 | return mp_ops.vcpu_is_preempted(cpu);
| ^
2 errors generated.
vim +/vcpu_is_preempted +346 arch/loongarch/kernel/paravirt.c
345
> 346 bool notrace vcpu_is_preempted(int cpu)
347 {
> 348 return mp_ops.vcpu_is_preempted(cpu);
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Hi, Bibo,
On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
>
> Function vcpu_is_preempted() is used to check whether vCPU is preempted
> or not. Here add implementation with vcpu_is_preempted() when option
> CONFIG_PARAVIRT is enabled.
>
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
> arch/loongarch/include/asm/smp.h | 1 +
> arch/loongarch/include/asm/spinlock.h | 5 +++++
> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
> arch/loongarch/kernel/smp.c | 6 ++++++
> 4 files changed, 28 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
> index 3a47f52959a8..5b37f7bf2060 100644
> --- a/arch/loongarch/include/asm/smp.h
> +++ b/arch/loongarch/include/asm/smp.h
> @@ -18,6 +18,7 @@ struct smp_ops {
> void (*init_ipi)(void);
> void (*send_ipi_single)(int cpu, unsigned int action);
> void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
> + bool (*vcpu_is_preempted)(int cpu);
> };
> extern struct smp_ops mp_ops;
>
> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
> index 7cb3476999be..c001cef893aa 100644
> --- a/arch/loongarch/include/asm/spinlock.h
> +++ b/arch/loongarch/include/asm/spinlock.h
> @@ -5,6 +5,11 @@
> #ifndef _ASM_SPINLOCK_H
> #define _ASM_SPINLOCK_H
>
> +#ifdef CONFIG_PARAVIRT
> +#define vcpu_is_preempted vcpu_is_preempted
> +bool vcpu_is_preempted(int cpu);
> +#endif
Maybe paravirt.h is a better place?
> +
> #include <asm/processor.h>
> #include <asm/qspinlock.h>
> #include <asm/qrwlock.h>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> index b1b51f920b23..b99404b6b13f 100644
> --- a/arch/loongarch/kernel/paravirt.c
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
> #ifdef CONFIG_SMP
> static struct smp_ops native_ops;
>
> +static bool pv_vcpu_is_preempted(int cpu)
> +{
> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> +
> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> +}
> +
> static void pv_send_ipi_single(int cpu, unsigned int action)
> {
> int min, old;
> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
> pr_err("Failed to install cpu hotplug callbacks\n");
> return r;
> }
> +
> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
> #endif
>
> static_call_update(pv_steal_clock, paravt_steal_clock);
> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
>
> return 0;
> }
> +
> +bool notrace vcpu_is_preempted(int cpu)
> +{
> + return mp_ops.vcpu_is_preempted(cpu);
> +}
We can simplify the whole patch like this, then we don't need to touch
smp.c, and we can merge Patch-2/3.
+bool notrace vcpu_is_preempted(int cpu)
+{
+ if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
+ return false;
+ else {
+ struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
+ return !!(src->preempted & KVM_VCPU_PREEMPTED);
+ }
+}
Huacai
> +EXPORT_SYMBOL(vcpu_is_preempted);
> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> index 46036d98da75..f04192fedf8d 100644
> --- a/arch/loongarch/kernel/smp.c
> +++ b/arch/loongarch/kernel/smp.c
> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
> panic("IPI IRQ request failed\n");
> }
>
> +static bool loongson_vcpu_is_preempted(int cpu)
> +{
> + return false;
> +}
> +
> struct smp_ops mp_ops = {
> .init_ipi = loongson_init_ipi,
> .send_ipi_single = loongson_send_ipi_single,
> .send_ipi_mask = loongson_send_ipi_mask,
> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
> };
>
> static void __init fdt_smp_setup(void)
> --
> 2.39.3
>
>
On 2025/11/18 下午8:48, Huacai Chen wrote:
> Hi, Bibo,
>
> On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>> Function vcpu_is_preempted() is used to check whether vCPU is preempted
>> or not. Here add implementation with vcpu_is_preempted() when option
>> CONFIG_PARAVIRT is enabled.
>>
>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>> ---
>> arch/loongarch/include/asm/smp.h | 1 +
>> arch/loongarch/include/asm/spinlock.h | 5 +++++
>> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
>> arch/loongarch/kernel/smp.c | 6 ++++++
>> 4 files changed, 28 insertions(+)
>>
>> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
>> index 3a47f52959a8..5b37f7bf2060 100644
>> --- a/arch/loongarch/include/asm/smp.h
>> +++ b/arch/loongarch/include/asm/smp.h
>> @@ -18,6 +18,7 @@ struct smp_ops {
>> void (*init_ipi)(void);
>> void (*send_ipi_single)(int cpu, unsigned int action);
>> void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
>> + bool (*vcpu_is_preempted)(int cpu);
>> };
>> extern struct smp_ops mp_ops;
>>
>> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
>> index 7cb3476999be..c001cef893aa 100644
>> --- a/arch/loongarch/include/asm/spinlock.h
>> +++ b/arch/loongarch/include/asm/spinlock.h
>> @@ -5,6 +5,11 @@
>> #ifndef _ASM_SPINLOCK_H
>> #define _ASM_SPINLOCK_H
>>
>> +#ifdef CONFIG_PARAVIRT
>> +#define vcpu_is_preempted vcpu_is_preempted
>> +bool vcpu_is_preempted(int cpu);
>> +#endif
> Maybe paravirt.h is a better place?
how about put it in asm/qspinlock.h since it is included by header file
asm/spinlock.h already?
>
>> +
>> #include <asm/processor.h>
>> #include <asm/qspinlock.h>
>> #include <asm/qrwlock.h>
>> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
>> index b1b51f920b23..b99404b6b13f 100644
>> --- a/arch/loongarch/kernel/paravirt.c
>> +++ b/arch/loongarch/kernel/paravirt.c
>> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
>> #ifdef CONFIG_SMP
>> static struct smp_ops native_ops;
>>
>> +static bool pv_vcpu_is_preempted(int cpu)
>> +{
>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>> +
>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
>> +}
>> +
>> static void pv_send_ipi_single(int cpu, unsigned int action)
>> {
>> int min, old;
>> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
>> pr_err("Failed to install cpu hotplug callbacks\n");
>> return r;
>> }
>> +
>> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
>> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
>> #endif
>>
>> static_call_update(pv_steal_clock, paravt_steal_clock);
>> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
>>
>> return 0;
>> }
>> +
>> +bool notrace vcpu_is_preempted(int cpu)
>> +{
>> + return mp_ops.vcpu_is_preempted(cpu);
>> +}
>
> We can simplify the whole patch like this, then we don't need to touch
> smp.c, and we can merge Patch-2/3.
>
> +bool notrace vcpu_is_preempted(int cpu)
> +{
> + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> + return false;
> + else {
> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> + }
> +}
> Huacai
>
>> +EXPORT_SYMBOL(vcpu_is_preempted);
>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
>> index 46036d98da75..f04192fedf8d 100644
>> --- a/arch/loongarch/kernel/smp.c
>> +++ b/arch/loongarch/kernel/smp.c
>> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
>> panic("IPI IRQ request failed\n");
>> }
>>
>> +static bool loongson_vcpu_is_preempted(int cpu)
>> +{
>> + return false;
>> +}
>> +
>> struct smp_ops mp_ops = {
>> .init_ipi = loongson_init_ipi,
>> .send_ipi_single = loongson_send_ipi_single,
>> .send_ipi_mask = loongson_send_ipi_mask,
>> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
>> };
>>
>> static void __init fdt_smp_setup(void)
>> --
>> 2.39.3
>>
>>
On Wed, Nov 19, 2025 at 10:53 AM Bibo Mao <maobibo@loongson.cn> wrote:
>
>
>
> On 2025/11/18 下午8:48, Huacai Chen wrote:
> > Hi, Bibo,
> >
> > On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
> >>
> >> Function vcpu_is_preempted() is used to check whether vCPU is preempted
> >> or not. Here add implementation with vcpu_is_preempted() when option
> >> CONFIG_PARAVIRT is enabled.
> >>
> >> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> >> ---
> >> arch/loongarch/include/asm/smp.h | 1 +
> >> arch/loongarch/include/asm/spinlock.h | 5 +++++
> >> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
> >> arch/loongarch/kernel/smp.c | 6 ++++++
> >> 4 files changed, 28 insertions(+)
> >>
> >> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
> >> index 3a47f52959a8..5b37f7bf2060 100644
> >> --- a/arch/loongarch/include/asm/smp.h
> >> +++ b/arch/loongarch/include/asm/smp.h
> >> @@ -18,6 +18,7 @@ struct smp_ops {
> >> void (*init_ipi)(void);
> >> void (*send_ipi_single)(int cpu, unsigned int action);
> >> void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
> >> + bool (*vcpu_is_preempted)(int cpu);
> >> };
> >> extern struct smp_ops mp_ops;
> >>
> >> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
> >> index 7cb3476999be..c001cef893aa 100644
> >> --- a/arch/loongarch/include/asm/spinlock.h
> >> +++ b/arch/loongarch/include/asm/spinlock.h
> >> @@ -5,6 +5,11 @@
> >> #ifndef _ASM_SPINLOCK_H
> >> #define _ASM_SPINLOCK_H
> >>
> >> +#ifdef CONFIG_PARAVIRT
> >> +#define vcpu_is_preempted vcpu_is_preempted
> >> +bool vcpu_is_preempted(int cpu);
> >> +#endif
> > Maybe paravirt.h is a better place?
> how about put it in asm/qspinlock.h since it is included by header file
> asm/spinlock.h already?
qspinlock.h is better than spinlock.h
Huacai
>
> >
> >> +
> >> #include <asm/processor.h>
> >> #include <asm/qspinlock.h>
> >> #include <asm/qrwlock.h>
> >> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> >> index b1b51f920b23..b99404b6b13f 100644
> >> --- a/arch/loongarch/kernel/paravirt.c
> >> +++ b/arch/loongarch/kernel/paravirt.c
> >> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
> >> #ifdef CONFIG_SMP
> >> static struct smp_ops native_ops;
> >>
> >> +static bool pv_vcpu_is_preempted(int cpu)
> >> +{
> >> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> >> +
> >> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> >> +}
> >> +
> >> static void pv_send_ipi_single(int cpu, unsigned int action)
> >> {
> >> int min, old;
> >> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
> >> pr_err("Failed to install cpu hotplug callbacks\n");
> >> return r;
> >> }
> >> +
> >> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> >> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
> >> #endif
> >>
> >> static_call_update(pv_steal_clock, paravt_steal_clock);
> >> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
> >>
> >> return 0;
> >> }
> >> +
> >> +bool notrace vcpu_is_preempted(int cpu)
> >> +{
> >> + return mp_ops.vcpu_is_preempted(cpu);
> >> +}
> >
> > We can simplify the whole patch like this, then we don't need to touch
> > smp.c, and we can merge Patch-2/3.
> >
> > +bool notrace vcpu_is_preempted(int cpu)
> > +{
> > + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> > + return false;
> > + else {
> > + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> > + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> > + }
> > +}
> > Huacai
> >
> >> +EXPORT_SYMBOL(vcpu_is_preempted);
> >> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> >> index 46036d98da75..f04192fedf8d 100644
> >> --- a/arch/loongarch/kernel/smp.c
> >> +++ b/arch/loongarch/kernel/smp.c
> >> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
> >> panic("IPI IRQ request failed\n");
> >> }
> >>
> >> +static bool loongson_vcpu_is_preempted(int cpu)
> >> +{
> >> + return false;
> >> +}
> >> +
> >> struct smp_ops mp_ops = {
> >> .init_ipi = loongson_init_ipi,
> >> .send_ipi_single = loongson_send_ipi_single,
> >> .send_ipi_mask = loongson_send_ipi_mask,
> >> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
> >> };
> >>
> >> static void __init fdt_smp_setup(void)
> >> --
> >> 2.39.3
> >>
> >>
>
>
On 2025/11/18 下午8:48, Huacai Chen wrote:
> Hi, Bibo,
>
> On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>> Function vcpu_is_preempted() is used to check whether vCPU is preempted
>> or not. Here add implementation with vcpu_is_preempted() when option
>> CONFIG_PARAVIRT is enabled.
>>
>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>> ---
>> arch/loongarch/include/asm/smp.h | 1 +
>> arch/loongarch/include/asm/spinlock.h | 5 +++++
>> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
>> arch/loongarch/kernel/smp.c | 6 ++++++
>> 4 files changed, 28 insertions(+)
>>
>> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
>> index 3a47f52959a8..5b37f7bf2060 100644
>> --- a/arch/loongarch/include/asm/smp.h
>> +++ b/arch/loongarch/include/asm/smp.h
>> @@ -18,6 +18,7 @@ struct smp_ops {
>> void (*init_ipi)(void);
>> void (*send_ipi_single)(int cpu, unsigned int action);
>> void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
>> + bool (*vcpu_is_preempted)(int cpu);
>> };
>> extern struct smp_ops mp_ops;
>>
>> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
>> index 7cb3476999be..c001cef893aa 100644
>> --- a/arch/loongarch/include/asm/spinlock.h
>> +++ b/arch/loongarch/include/asm/spinlock.h
>> @@ -5,6 +5,11 @@
>> #ifndef _ASM_SPINLOCK_H
>> #define _ASM_SPINLOCK_H
>>
>> +#ifdef CONFIG_PARAVIRT
>> +#define vcpu_is_preempted vcpu_is_preempted
>> +bool vcpu_is_preempted(int cpu);
>> +#endif
> Maybe paravirt.h is a better place?
It is actually a little strange to add macro CONFIG_PARAVIRT in file
asm/spinlock.h
vcpu_is_preempted is originally defined in header file
include/linux/sched.h like this
#ifndef vcpu_is_preempted
static inline bool vcpu_is_preempted(int cpu)
{
return false;
}
#endif
that requires that header file is included before sched.h, file
asm/spinlock.h can meet this requirement, however header file paravirt.h
maybe it is not included before sched.h in generic.
Here vcpu_is_preempted definition is added before the following including.
#include <asm/processor.h>
#include <asm/qspinlock.h>
#include <asm/qrwlock.h>
Maybe it is better to be added after the above header files including
sentences, but need further investigation.
>
>> +
>> #include <asm/processor.h>
>> #include <asm/qspinlock.h>
>> #include <asm/qrwlock.h>
>> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
>> index b1b51f920b23..b99404b6b13f 100644
>> --- a/arch/loongarch/kernel/paravirt.c
>> +++ b/arch/loongarch/kernel/paravirt.c
>> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
>> #ifdef CONFIG_SMP
>> static struct smp_ops native_ops;
>>
>> +static bool pv_vcpu_is_preempted(int cpu)
>> +{
>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>> +
>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
>> +}
>> +
>> static void pv_send_ipi_single(int cpu, unsigned int action)
>> {
>> int min, old;
>> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
>> pr_err("Failed to install cpu hotplug callbacks\n");
>> return r;
>> }
>> +
>> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
>> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
>> #endif
>>
>> static_call_update(pv_steal_clock, paravt_steal_clock);
>> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
>>
>> return 0;
>> }
>> +
>> +bool notrace vcpu_is_preempted(int cpu)
>> +{
>> + return mp_ops.vcpu_is_preempted(cpu);
>> +}
>
> We can simplify the whole patch like this, then we don't need to touch
> smp.c, and we can merge Patch-2/3.
>
> +bool notrace vcpu_is_preempted(int cpu)
> +{
> + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> + return false;
> + else {
> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> + }
> +}
1. there is assembly output about relative vcpu_is_preempted
<loongson_vcpu_is_preempted>:
move $r4,$r0
jirl $r0,$r1,0
<pv_vcpu_is_preempted>:
pcalau12i $r13,8759(0x2237)
slli.d $r4,$r4,0x3
addi.d $r13,$r13,-1000(0xc18)
ldx.d $r13,$r13,$r4
pcalau12i $r12,5462(0x1556)
addi.d $r12,$r12,384(0x180)
add.d $r12,$r13,$r12
ld.bu $r4,$r12,16(0x10)
andi $r4,$r4,0x1
jirl $r0,$r1,0
<vcpu_is_preempted>:
pcalau12i $r12,8775(0x2247)
ld.d $r12,$r12,-472(0xe28)
jirl $r0,$r12,0
andi $r0,$r0,0x0
<vcpu_is_preempted_new>:
pcalau12i $r12,8151(0x1fd7)
ld.d $r12,$r12,-1008(0xc10)
bstrpick.d $r12,$r12,0x1a,0x1a
beqz $r12,188(0xbc) # 900000000024ec60
pcalau12i $r12,11802(0x2e1a)
addi.d $r12,$r12,-1400(0xa88)
ldptr.w $r14,$r12,36(0x24)
beqz $r14,108(0x6c) # 900000000024ec20
addi.w $r13,$r0,1(0x1)
bne $r14,$r13,164(0xa4) # 900000000024ec60
ldptr.w $r13,$r12,40(0x28)
bnez $r13,24(0x18) # 900000000024ebdc
lu12i.w $r14,262144(0x40000)
ori $r14,$r14,0x4
cpucfg $r14,$r14
slli.w $r13,$r14,0x0
st.w $r14,$r12,40(0x28)
bstrpick.d $r13,$r13,0x3,0x3
beqz $r13,128(0x80) # 900000000024ec60
pcalau12i $r13,8759(0x2237)
slli.d $r4,$r4,0x3
addi.d $r13,$r13,-1000(0xc18)
ldx.d $r13,$r13,$r4
pcalau12i $r12,5462(0x1556)
addi.d $r12,$r12,384(0x180)
add.d $r12,$r13,$r12
ld.bu $r4,$r12,16(0x10)
andi $r4,$r4,0x1
jirl $r0,$r1,0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
lu12i.w $r13,262144(0x40000)
cpucfg $r13,$r13
lu12i.w $r15,1237(0x4d5)
ori $r15,$r15,0x64b
slli.w $r13,$r13,0x0
bne $r13,$r15,-124(0x3ff84) # 900000000024ebb8
addi.w $r13,$r0,1(0x1)
st.w $r13,$r12,36(0x24)
b -128(0xfffff80) # 900000000024ebc0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
andi $r0,$r0,0x0
move $r4,$r0
jirl $r0,$r1,0
With vcpu_is_preempted(), there is one memory load and one jirl jump,
with vcpu_is_preempted_new(), there is two memory load and two beq
compare instructions.
2. In some scenery such nr_cpus == 1, loongson_vcpu_is_preempted() is
better than pv_vcpu_is_preempted() even if the preempt feature is enabled.
Regards
Bibo Mao
> Huacai
>
>> +EXPORT_SYMBOL(vcpu_is_preempted);
>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
>> index 46036d98da75..f04192fedf8d 100644
>> --- a/arch/loongarch/kernel/smp.c
>> +++ b/arch/loongarch/kernel/smp.c
>> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
>> panic("IPI IRQ request failed\n");
>> }
>>
>> +static bool loongson_vcpu_is_preempted(int cpu)
>> +{
>> + return false;
>> +}
>> +
>> struct smp_ops mp_ops = {
>> .init_ipi = loongson_init_ipi,
>> .send_ipi_single = loongson_send_ipi_single,
>> .send_ipi_mask = loongson_send_ipi_mask,
>> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
>> };
>>
>> static void __init fdt_smp_setup(void)
>> --
>> 2.39.3
>>
>>
On 2025/11/19 上午9:59, Bibo Mao wrote:
>
>
> On 2025/11/18 下午8:48, Huacai Chen wrote:
>> Hi, Bibo,
>>
>> On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>>
>>> Function vcpu_is_preempted() is used to check whether vCPU is preempted
>>> or not. Here add implementation with vcpu_is_preempted() when option
>>> CONFIG_PARAVIRT is enabled.
>>>
>>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>>> ---
>>> arch/loongarch/include/asm/smp.h | 1 +
>>> arch/loongarch/include/asm/spinlock.h | 5 +++++
>>> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
>>> arch/loongarch/kernel/smp.c | 6 ++++++
>>> 4 files changed, 28 insertions(+)
>>>
>>> diff --git a/arch/loongarch/include/asm/smp.h
>>> b/arch/loongarch/include/asm/smp.h
>>> index 3a47f52959a8..5b37f7bf2060 100644
>>> --- a/arch/loongarch/include/asm/smp.h
>>> +++ b/arch/loongarch/include/asm/smp.h
>>> @@ -18,6 +18,7 @@ struct smp_ops {
>>> void (*init_ipi)(void);
>>> void (*send_ipi_single)(int cpu, unsigned int action);
>>> void (*send_ipi_mask)(const struct cpumask *mask, unsigned
>>> int action);
>>> + bool (*vcpu_is_preempted)(int cpu);
>>> };
>>> extern struct smp_ops mp_ops;
>>>
>>> diff --git a/arch/loongarch/include/asm/spinlock.h
>>> b/arch/loongarch/include/asm/spinlock.h
>>> index 7cb3476999be..c001cef893aa 100644
>>> --- a/arch/loongarch/include/asm/spinlock.h
>>> +++ b/arch/loongarch/include/asm/spinlock.h
>>> @@ -5,6 +5,11 @@
>>> #ifndef _ASM_SPINLOCK_H
>>> #define _ASM_SPINLOCK_H
>>>
>>> +#ifdef CONFIG_PARAVIRT
>>> +#define vcpu_is_preempted vcpu_is_preempted
>>> +bool vcpu_is_preempted(int cpu);
>>> +#endif
>> Maybe paravirt.h is a better place?
>
> It is actually a little strange to add macro CONFIG_PARAVIRT in file
> asm/spinlock.h
>
> vcpu_is_preempted is originally defined in header file
> include/linux/sched.h like this
> #ifndef vcpu_is_preempted
> static inline bool vcpu_is_preempted(int cpu)
> {
> return false;
> }
> #endif
>
> that requires that header file is included before sched.h, file
> asm/spinlock.h can meet this requirement, however header file paravirt.h
> maybe it is not included before sched.h in generic.
>
> Here vcpu_is_preempted definition is added before the following including.
> #include <asm/processor.h>
> #include <asm/qspinlock.h>
> #include <asm/qrwlock.h>
> Maybe it is better to be added after the above header files including
> sentences, but need further investigation.
>>
>>> +
>>> #include <asm/processor.h>
>>> #include <asm/qspinlock.h>
>>> #include <asm/qrwlock.h>
>>> diff --git a/arch/loongarch/kernel/paravirt.c
>>> b/arch/loongarch/kernel/paravirt.c
>>> index b1b51f920b23..b99404b6b13f 100644
>>> --- a/arch/loongarch/kernel/paravirt.c
>>> +++ b/arch/loongarch/kernel/paravirt.c
>>> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
>>> #ifdef CONFIG_SMP
>>> static struct smp_ops native_ops;
>>>
>>> +static bool pv_vcpu_is_preempted(int cpu)
>>> +{
>>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>>> +
>>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
>>> +}
>>> +
>>> static void pv_send_ipi_single(int cpu, unsigned int action)
>>> {
>>> int min, old;
>>> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
>>> pr_err("Failed to install cpu hotplug callbacks\n");
>>> return r;
>>> }
>>> +
>>> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
>>> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
>>> #endif
>>>
>>> static_call_update(pv_steal_clock, paravt_steal_clock);
>>> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
>>>
>>> return 0;
>>> }
>>> +
>>> +bool notrace vcpu_is_preempted(int cpu)
>>> +{
>>> + return mp_ops.vcpu_is_preempted(cpu);
>>> +}
>>
>> We can simplify the whole patch like this, then we don't need to touch
>> smp.c, and we can merge Patch-2/3.
>>
>> +bool notrace vcpu_is_preempted(int cpu)
>> +{
>> + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
>> + return false;
>> + else {
>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
>> + }
>> +}
> 1. there is assembly output about relative vcpu_is_preempted
> <loongson_vcpu_is_preempted>:
> move $r4,$r0
> jirl $r0,$r1,0
>
> <pv_vcpu_is_preempted>:
> pcalau12i $r13,8759(0x2237)
> slli.d $r4,$r4,0x3
> addi.d $r13,$r13,-1000(0xc18)
> ldx.d $r13,$r13,$r4
> pcalau12i $r12,5462(0x1556)
> addi.d $r12,$r12,384(0x180)
> add.d $r12,$r13,$r12
> ld.bu $r4,$r12,16(0x10)
> andi $r4,$r4,0x1
> jirl $r0,$r1,0
>
> <vcpu_is_preempted>:
> pcalau12i $r12,8775(0x2247)
> ld.d $r12,$r12,-472(0xe28)
> jirl $r0,$r12,0
> andi $r0,$r0,0x0
>
> <vcpu_is_preempted_new>:
> pcalau12i $r12,8151(0x1fd7)
> ld.d $r12,$r12,-1008(0xc10)
> bstrpick.d $r12,$r12,0x1a,0x1a
> beqz $r12,188(0xbc) # 900000000024ec60
> pcalau12i $r12,11802(0x2e1a)
> addi.d $r12,$r12,-1400(0xa88)
> ldptr.w $r14,$r12,36(0x24)
> beqz $r14,108(0x6c) # 900000000024ec20
> addi.w $r13,$r0,1(0x1)
> bne $r14,$r13,164(0xa4) # 900000000024ec60
> ldptr.w $r13,$r12,40(0x28)
> bnez $r13,24(0x18) # 900000000024ebdc
> lu12i.w $r14,262144(0x40000)
> ori $r14,$r14,0x4
> cpucfg $r14,$r14
> slli.w $r13,$r14,0x0
> st.w $r14,$r12,40(0x28)
> bstrpick.d $r13,$r13,0x3,0x3
> beqz $r13,128(0x80) # 900000000024ec60
> pcalau12i $r13,8759(0x2237)
> slli.d $r4,$r4,0x3
> addi.d $r13,$r13,-1000(0xc18)
> ldx.d $r13,$r13,$r4
> pcalau12i $r12,5462(0x1556)
> addi.d $r12,$r12,384(0x180)
> add.d $r12,$r13,$r12
> ld.bu $r4,$r12,16(0x10)
> andi $r4,$r4,0x1
> jirl $r0,$r1,0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> lu12i.w $r13,262144(0x40000)
> cpucfg $r13,$r13
> lu12i.w $r15,1237(0x4d5)
> ori $r15,$r15,0x64b
> slli.w $r13,$r13,0x0
> bne $r13,$r15,-124(0x3ff84) # 900000000024ebb8
> addi.w $r13,$r0,1(0x1)
> st.w $r13,$r12,36(0x24)
> b -128(0xfffff80) # 900000000024ebc0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> move $r4,$r0
> jirl $r0,$r1,0
>
> With vcpu_is_preempted(), there is one memory load and one jirl jump,
> with vcpu_is_preempted_new(), there is two memory load and two beq
> compare instructions.
>
> 2. In some scenery such nr_cpus == 1, loongson_vcpu_is_preempted() is
> better than pv_vcpu_is_preempted() even if the preempt feature is enabled.
how about use static key and keep file smp.c untouched?
bool notrace vcpu_is_preempted(int cpu)
{
struct kvm_steal_time *src;
if (!static_branch_unlikely(&virt_preempt_key))
return false;
src = &per_cpu(steal_time, cpu);
return !!(src->preempted & KVM_VCPU_PREEMPTED);
}
it reduces one memory load, here is assembly output:
<vcpu_is_preempted>:
andi $r0,$r0,0x0
move $r4,$r0
jirl $r0,$r1,0
andi $r0,$r0,0x0
pcalau12i $r13,8759(0x2237)
slli.d $r4,$r4,0x3
addi.d $r13,$r13,-1000(0xc18)
ldx.d $r13,$r13,$r4
pcalau12i $r12,5462(0x1556)
addi.d $r12,$r12,384(0x180)
add.d $r12,$r13,$r12
ld.bu $r4,$r12,16(0x10)
andi $r4,$r4,0x1
jirl $r0,$r1,0
Regards
Bibo Mao
>
> Regards
> Bibo Mao
>> Huacai
>>
>>> +EXPORT_SYMBOL(vcpu_is_preempted);
>>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
>>> index 46036d98da75..f04192fedf8d 100644
>>> --- a/arch/loongarch/kernel/smp.c
>>> +++ b/arch/loongarch/kernel/smp.c
>>> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
>>> panic("IPI IRQ request failed\n");
>>> }
>>>
>>> +static bool loongson_vcpu_is_preempted(int cpu)
>>> +{
>>> + return false;
>>> +}
>>> +
>>> struct smp_ops mp_ops = {
>>> .init_ipi = loongson_init_ipi,
>>> .send_ipi_single = loongson_send_ipi_single,
>>> .send_ipi_mask = loongson_send_ipi_mask,
>>> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
>>> };
>>>
>>> static void __init fdt_smp_setup(void)
>>> --
>>> 2.39.3
>>>
>>>
>
On Wed, Nov 19, 2025 at 2:12 PM Bibo Mao <maobibo@loongson.cn> wrote:
>
>
>
> On 2025/11/19 上午9:59, Bibo Mao wrote:
> >
> >
> > On 2025/11/18 下午8:48, Huacai Chen wrote:
> >> Hi, Bibo,
> >>
> >> On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
> >>>
> >>> Function vcpu_is_preempted() is used to check whether vCPU is preempted
> >>> or not. Here add implementation with vcpu_is_preempted() when option
> >>> CONFIG_PARAVIRT is enabled.
> >>>
> >>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> >>> ---
> >>> arch/loongarch/include/asm/smp.h | 1 +
> >>> arch/loongarch/include/asm/spinlock.h | 5 +++++
> >>> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
> >>> arch/loongarch/kernel/smp.c | 6 ++++++
> >>> 4 files changed, 28 insertions(+)
> >>>
> >>> diff --git a/arch/loongarch/include/asm/smp.h
> >>> b/arch/loongarch/include/asm/smp.h
> >>> index 3a47f52959a8..5b37f7bf2060 100644
> >>> --- a/arch/loongarch/include/asm/smp.h
> >>> +++ b/arch/loongarch/include/asm/smp.h
> >>> @@ -18,6 +18,7 @@ struct smp_ops {
> >>> void (*init_ipi)(void);
> >>> void (*send_ipi_single)(int cpu, unsigned int action);
> >>> void (*send_ipi_mask)(const struct cpumask *mask, unsigned
> >>> int action);
> >>> + bool (*vcpu_is_preempted)(int cpu);
> >>> };
> >>> extern struct smp_ops mp_ops;
> >>>
> >>> diff --git a/arch/loongarch/include/asm/spinlock.h
> >>> b/arch/loongarch/include/asm/spinlock.h
> >>> index 7cb3476999be..c001cef893aa 100644
> >>> --- a/arch/loongarch/include/asm/spinlock.h
> >>> +++ b/arch/loongarch/include/asm/spinlock.h
> >>> @@ -5,6 +5,11 @@
> >>> #ifndef _ASM_SPINLOCK_H
> >>> #define _ASM_SPINLOCK_H
> >>>
> >>> +#ifdef CONFIG_PARAVIRT
> >>> +#define vcpu_is_preempted vcpu_is_preempted
> >>> +bool vcpu_is_preempted(int cpu);
> >>> +#endif
> >> Maybe paravirt.h is a better place?
> >
> > It is actually a little strange to add macro CONFIG_PARAVIRT in file
> > asm/spinlock.h
> >
> > vcpu_is_preempted is originally defined in header file
> > include/linux/sched.h like this
> > #ifndef vcpu_is_preempted
> > static inline bool vcpu_is_preempted(int cpu)
> > {
> > return false;
> > }
> > #endif
> >
> > that requires that header file is included before sched.h, file
> > asm/spinlock.h can meet this requirement, however header file paravirt.h
> > maybe it is not included before sched.h in generic.
> >
> > Here vcpu_is_preempted definition is added before the following including.
> > #include <asm/processor.h>
> > #include <asm/qspinlock.h>
> > #include <asm/qrwlock.h>
> > Maybe it is better to be added after the above header files including
> > sentences, but need further investigation.
> >>
> >>> +
> >>> #include <asm/processor.h>
> >>> #include <asm/qspinlock.h>
> >>> #include <asm/qrwlock.h>
> >>> diff --git a/arch/loongarch/kernel/paravirt.c
> >>> b/arch/loongarch/kernel/paravirt.c
> >>> index b1b51f920b23..b99404b6b13f 100644
> >>> --- a/arch/loongarch/kernel/paravirt.c
> >>> +++ b/arch/loongarch/kernel/paravirt.c
> >>> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
> >>> #ifdef CONFIG_SMP
> >>> static struct smp_ops native_ops;
> >>>
> >>> +static bool pv_vcpu_is_preempted(int cpu)
> >>> +{
> >>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> >>> +
> >>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> >>> +}
> >>> +
> >>> static void pv_send_ipi_single(int cpu, unsigned int action)
> >>> {
> >>> int min, old;
> >>> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
> >>> pr_err("Failed to install cpu hotplug callbacks\n");
> >>> return r;
> >>> }
> >>> +
> >>> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> >>> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
> >>> #endif
> >>>
> >>> static_call_update(pv_steal_clock, paravt_steal_clock);
> >>> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
> >>>
> >>> return 0;
> >>> }
> >>> +
> >>> +bool notrace vcpu_is_preempted(int cpu)
> >>> +{
> >>> + return mp_ops.vcpu_is_preempted(cpu);
> >>> +}
> >>
> >> We can simplify the whole patch like this, then we don't need to touch
> >> smp.c, and we can merge Patch-2/3.
> >>
> >> +bool notrace vcpu_is_preempted(int cpu)
> >> +{
> >> + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> >> + return false;
> >> + else {
> >> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> >> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> >> + }
> >> +}
> > 1. there is assembly output about relative vcpu_is_preempted
> > <loongson_vcpu_is_preempted>:
> > move $r4,$r0
> > jirl $r0,$r1,0
> >
> > <pv_vcpu_is_preempted>:
> > pcalau12i $r13,8759(0x2237)
> > slli.d $r4,$r4,0x3
> > addi.d $r13,$r13,-1000(0xc18)
> > ldx.d $r13,$r13,$r4
> > pcalau12i $r12,5462(0x1556)
> > addi.d $r12,$r12,384(0x180)
> > add.d $r12,$r13,$r12
> > ld.bu $r4,$r12,16(0x10)
> > andi $r4,$r4,0x1
> > jirl $r0,$r1,0
> >
> > <vcpu_is_preempted>:
> > pcalau12i $r12,8775(0x2247)
> > ld.d $r12,$r12,-472(0xe28)
> > jirl $r0,$r12,0
> > andi $r0,$r0,0x0
> >
> > <vcpu_is_preempted_new>:
> > pcalau12i $r12,8151(0x1fd7)
> > ld.d $r12,$r12,-1008(0xc10)
> > bstrpick.d $r12,$r12,0x1a,0x1a
> > beqz $r12,188(0xbc) # 900000000024ec60
> > pcalau12i $r12,11802(0x2e1a)
> > addi.d $r12,$r12,-1400(0xa88)
> > ldptr.w $r14,$r12,36(0x24)
> > beqz $r14,108(0x6c) # 900000000024ec20
> > addi.w $r13,$r0,1(0x1)
> > bne $r14,$r13,164(0xa4) # 900000000024ec60
> > ldptr.w $r13,$r12,40(0x28)
> > bnez $r13,24(0x18) # 900000000024ebdc
> > lu12i.w $r14,262144(0x40000)
> > ori $r14,$r14,0x4
> > cpucfg $r14,$r14
> > slli.w $r13,$r14,0x0
> > st.w $r14,$r12,40(0x28)
> > bstrpick.d $r13,$r13,0x3,0x3
> > beqz $r13,128(0x80) # 900000000024ec60
> > pcalau12i $r13,8759(0x2237)
> > slli.d $r4,$r4,0x3
> > addi.d $r13,$r13,-1000(0xc18)
> > ldx.d $r13,$r13,$r4
> > pcalau12i $r12,5462(0x1556)
> > addi.d $r12,$r12,384(0x180)
> > add.d $r12,$r13,$r12
> > ld.bu $r4,$r12,16(0x10)
> > andi $r4,$r4,0x1
> > jirl $r0,$r1,0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > lu12i.w $r13,262144(0x40000)
> > cpucfg $r13,$r13
> > lu12i.w $r15,1237(0x4d5)
> > ori $r15,$r15,0x64b
> > slli.w $r13,$r13,0x0
> > bne $r13,$r15,-124(0x3ff84) # 900000000024ebb8
> > addi.w $r13,$r0,1(0x1)
> > st.w $r13,$r12,36(0x24)
> > b -128(0xfffff80) # 900000000024ebc0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > andi $r0,$r0,0x0
> > move $r4,$r0
> > jirl $r0,$r1,0
> >
> > With vcpu_is_preempted(), there is one memory load and one jirl jump,
> > with vcpu_is_preempted_new(), there is two memory load and two beq
> > compare instructions.
> >
> > 2. In some scenery such nr_cpus == 1, loongson_vcpu_is_preempted() is
> > better than pv_vcpu_is_preempted() even if the preempt feature is enabled.
> how about use static key and keep file smp.c untouched?
OK, it's better.
Huacai
> bool notrace vcpu_is_preempted(int cpu)
> {
> struct kvm_steal_time *src;
>
> if (!static_branch_unlikely(&virt_preempt_key))
> return false;
>
> src = &per_cpu(steal_time, cpu);
> return !!(src->preempted & KVM_VCPU_PREEMPTED);
> }
>
> it reduces one memory load, here is assembly output:
> <vcpu_is_preempted>:
> andi $r0,$r0,0x0
> move $r4,$r0
> jirl $r0,$r1,0
> andi $r0,$r0,0x0
> pcalau12i $r13,8759(0x2237)
> slli.d $r4,$r4,0x3
> addi.d $r13,$r13,-1000(0xc18)
> ldx.d $r13,$r13,$r4
> pcalau12i $r12,5462(0x1556)
> addi.d $r12,$r12,384(0x180)
> add.d $r12,$r13,$r12
> ld.bu $r4,$r12,16(0x10)
> andi $r4,$r4,0x1
> jirl $r0,$r1,0
>
> Regards
> Bibo Mao
>
> >
> > Regards
> > Bibo Mao
> >> Huacai
> >>
> >>> +EXPORT_SYMBOL(vcpu_is_preempted);
> >>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> >>> index 46036d98da75..f04192fedf8d 100644
> >>> --- a/arch/loongarch/kernel/smp.c
> >>> +++ b/arch/loongarch/kernel/smp.c
> >>> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
> >>> panic("IPI IRQ request failed\n");
> >>> }
> >>>
> >>> +static bool loongson_vcpu_is_preempted(int cpu)
> >>> +{
> >>> + return false;
> >>> +}
> >>> +
> >>> struct smp_ops mp_ops = {
> >>> .init_ipi = loongson_init_ipi,
> >>> .send_ipi_single = loongson_send_ipi_single,
> >>> .send_ipi_mask = loongson_send_ipi_mask,
> >>> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
> >>> };
> >>>
> >>> static void __init fdt_smp_setup(void)
> >>> --
> >>> 2.39.3
> >>>
> >>>
> >
>
>
On Wed, Nov 19, 2025 at 10:01 AM Bibo Mao <maobibo@loongson.cn> wrote:
>
>
>
> On 2025/11/18 下午8:48, Huacai Chen wrote:
> > Hi, Bibo,
> >
> > On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
> >>
> >> Function vcpu_is_preempted() is used to check whether vCPU is preempted
> >> or not. Here add implementation with vcpu_is_preempted() when option
> >> CONFIG_PARAVIRT is enabled.
> >>
> >> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> >> ---
> >> arch/loongarch/include/asm/smp.h | 1 +
> >> arch/loongarch/include/asm/spinlock.h | 5 +++++
> >> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
> >> arch/loongarch/kernel/smp.c | 6 ++++++
> >> 4 files changed, 28 insertions(+)
> >>
> >> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
> >> index 3a47f52959a8..5b37f7bf2060 100644
> >> --- a/arch/loongarch/include/asm/smp.h
> >> +++ b/arch/loongarch/include/asm/smp.h
> >> @@ -18,6 +18,7 @@ struct smp_ops {
> >> void (*init_ipi)(void);
> >> void (*send_ipi_single)(int cpu, unsigned int action);
> >> void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
> >> + bool (*vcpu_is_preempted)(int cpu);
> >> };
> >> extern struct smp_ops mp_ops;
> >>
> >> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
> >> index 7cb3476999be..c001cef893aa 100644
> >> --- a/arch/loongarch/include/asm/spinlock.h
> >> +++ b/arch/loongarch/include/asm/spinlock.h
> >> @@ -5,6 +5,11 @@
> >> #ifndef _ASM_SPINLOCK_H
> >> #define _ASM_SPINLOCK_H
> >>
> >> +#ifdef CONFIG_PARAVIRT
> >> +#define vcpu_is_preempted vcpu_is_preempted
> >> +bool vcpu_is_preempted(int cpu);
> >> +#endif
> > Maybe paravirt.h is a better place?
>
> It is actually a little strange to add macro CONFIG_PARAVIRT in file
> asm/spinlock.h
>
> vcpu_is_preempted is originally defined in header file
> include/linux/sched.h like this
> #ifndef vcpu_is_preempted
> static inline bool vcpu_is_preempted(int cpu)
> {
> return false;
> }
> #endif
>
> that requires that header file is included before sched.h, file
> asm/spinlock.h can meet this requirement, however header file paravirt.h
> maybe it is not included before sched.h in generic.
>
> Here vcpu_is_preempted definition is added before the following including.
> #include <asm/processor.h>
> #include <asm/qspinlock.h>
> #include <asm/qrwlock.h>
> Maybe it is better to be added after the above header files including
> sentences, but need further investigation.
powerpc put it in paravirt.h, so I think it is possible.
> >
> >> +
> >> #include <asm/processor.h>
> >> #include <asm/qspinlock.h>
> >> #include <asm/qrwlock.h>
> >> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> >> index b1b51f920b23..b99404b6b13f 100644
> >> --- a/arch/loongarch/kernel/paravirt.c
> >> +++ b/arch/loongarch/kernel/paravirt.c
> >> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
> >> #ifdef CONFIG_SMP
> >> static struct smp_ops native_ops;
> >>
> >> +static bool pv_vcpu_is_preempted(int cpu)
> >> +{
> >> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> >> +
> >> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> >> +}
> >> +
> >> static void pv_send_ipi_single(int cpu, unsigned int action)
> >> {
> >> int min, old;
> >> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
> >> pr_err("Failed to install cpu hotplug callbacks\n");
> >> return r;
> >> }
> >> +
> >> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> >> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
> >> #endif
> >>
> >> static_call_update(pv_steal_clock, paravt_steal_clock);
> >> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
> >>
> >> return 0;
> >> }
> >> +
> >> +bool notrace vcpu_is_preempted(int cpu)
> >> +{
> >> + return mp_ops.vcpu_is_preempted(cpu);
> >> +}
> >
> > We can simplify the whole patch like this, then we don't need to touch
> > smp.c, and we can merge Patch-2/3.
> >
> > +bool notrace vcpu_is_preempted(int cpu)
> > +{
> > + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
> > + return false;
> > + else {
> > + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> > + return !!(src->preempted & KVM_VCPU_PREEMPTED);
> > + }
> > +}
> 1. there is assembly output about relative vcpu_is_preempted
> <loongson_vcpu_is_preempted>:
> move $r4,$r0
> jirl $r0,$r1,0
>
> <pv_vcpu_is_preempted>:
> pcalau12i $r13,8759(0x2237)
> slli.d $r4,$r4,0x3
> addi.d $r13,$r13,-1000(0xc18)
> ldx.d $r13,$r13,$r4
> pcalau12i $r12,5462(0x1556)
> addi.d $r12,$r12,384(0x180)
> add.d $r12,$r13,$r12
> ld.bu $r4,$r12,16(0x10)
> andi $r4,$r4,0x1
> jirl $r0,$r1,0
>
> <vcpu_is_preempted>:
> pcalau12i $r12,8775(0x2247)
> ld.d $r12,$r12,-472(0xe28)
> jirl $r0,$r12,0
> andi $r0,$r0,0x0
>
> <vcpu_is_preempted_new>:
> pcalau12i $r12,8151(0x1fd7)
> ld.d $r12,$r12,-1008(0xc10)
> bstrpick.d $r12,$r12,0x1a,0x1a
> beqz $r12,188(0xbc) # 900000000024ec60
> pcalau12i $r12,11802(0x2e1a)
> addi.d $r12,$r12,-1400(0xa88)
> ldptr.w $r14,$r12,36(0x24)
> beqz $r14,108(0x6c) # 900000000024ec20
> addi.w $r13,$r0,1(0x1)
> bne $r14,$r13,164(0xa4) # 900000000024ec60
> ldptr.w $r13,$r12,40(0x28)
> bnez $r13,24(0x18) # 900000000024ebdc
> lu12i.w $r14,262144(0x40000)
> ori $r14,$r14,0x4
> cpucfg $r14,$r14
> slli.w $r13,$r14,0x0
> st.w $r14,$r12,40(0x28)
> bstrpick.d $r13,$r13,0x3,0x3
> beqz $r13,128(0x80) # 900000000024ec60
> pcalau12i $r13,8759(0x2237)
> slli.d $r4,$r4,0x3
> addi.d $r13,$r13,-1000(0xc18)
> ldx.d $r13,$r13,$r4
> pcalau12i $r12,5462(0x1556)
> addi.d $r12,$r12,384(0x180)
> add.d $r12,$r13,$r12
> ld.bu $r4,$r12,16(0x10)
> andi $r4,$r4,0x1
> jirl $r0,$r1,0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> lu12i.w $r13,262144(0x40000)
> cpucfg $r13,$r13
> lu12i.w $r15,1237(0x4d5)
> ori $r15,$r15,0x64b
> slli.w $r13,$r13,0x0
> bne $r13,$r15,-124(0x3ff84) # 900000000024ebb8
> addi.w $r13,$r0,1(0x1)
> st.w $r13,$r12,36(0x24)
> b -128(0xfffff80) # 900000000024ebc0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> andi $r0,$r0,0x0
> move $r4,$r0
> jirl $r0,$r1,0
>
> With vcpu_is_preempted(), there is one memory load and one jirl jump,
> with vcpu_is_preempted_new(), there is two memory load and two beq
> compare instructions.
Is vcpu_is_preempted() performance critical (we need performance data
here)? It seems the powerpc version is also complex.
>
> 2. In some scenery such nr_cpus == 1, loongson_vcpu_is_preempted() is
> better than pv_vcpu_is_preempted() even if the preempt feature is enabled.
In your original patch, "mp_ops.vcpu_is_preempted =
pv_vcpu_is_preempted" if the preempt feature is enabled. Why is
loongson_vcpu_is_preempted() called when nr_cpus=1?
Huacai
>
> Regards
> Bibo Mao
> > Huacai
> >
> >> +EXPORT_SYMBOL(vcpu_is_preempted);
> >> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> >> index 46036d98da75..f04192fedf8d 100644
> >> --- a/arch/loongarch/kernel/smp.c
> >> +++ b/arch/loongarch/kernel/smp.c
> >> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
> >> panic("IPI IRQ request failed\n");
> >> }
> >>
> >> +static bool loongson_vcpu_is_preempted(int cpu)
> >> +{
> >> + return false;
> >> +}
> >> +
> >> struct smp_ops mp_ops = {
> >> .init_ipi = loongson_init_ipi,
> >> .send_ipi_single = loongson_send_ipi_single,
> >> .send_ipi_mask = loongson_send_ipi_mask,
> >> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
> >> };
> >>
> >> static void __init fdt_smp_setup(void)
> >> --
> >> 2.39.3
> >>
> >>
>
>
On 2025/11/19 上午10:58, Huacai Chen wrote:
> On Wed, Nov 19, 2025 at 10:01 AM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>>
>>
>> On 2025/11/18 下午8:48, Huacai Chen wrote:
>>> Hi, Bibo,
>>>
>>> On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>>>
>>>> Function vcpu_is_preempted() is used to check whether vCPU is preempted
>>>> or not. Here add implementation with vcpu_is_preempted() when option
>>>> CONFIG_PARAVIRT is enabled.
>>>>
>>>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>>>> ---
>>>> arch/loongarch/include/asm/smp.h | 1 +
>>>> arch/loongarch/include/asm/spinlock.h | 5 +++++
>>>> arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++
>>>> arch/loongarch/kernel/smp.c | 6 ++++++
>>>> 4 files changed, 28 insertions(+)
>>>>
>>>> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
>>>> index 3a47f52959a8..5b37f7bf2060 100644
>>>> --- a/arch/loongarch/include/asm/smp.h
>>>> +++ b/arch/loongarch/include/asm/smp.h
>>>> @@ -18,6 +18,7 @@ struct smp_ops {
>>>> void (*init_ipi)(void);
>>>> void (*send_ipi_single)(int cpu, unsigned int action);
>>>> void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
>>>> + bool (*vcpu_is_preempted)(int cpu);
>>>> };
>>>> extern struct smp_ops mp_ops;
>>>>
>>>> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
>>>> index 7cb3476999be..c001cef893aa 100644
>>>> --- a/arch/loongarch/include/asm/spinlock.h
>>>> +++ b/arch/loongarch/include/asm/spinlock.h
>>>> @@ -5,6 +5,11 @@
>>>> #ifndef _ASM_SPINLOCK_H
>>>> #define _ASM_SPINLOCK_H
>>>>
>>>> +#ifdef CONFIG_PARAVIRT
>>>> +#define vcpu_is_preempted vcpu_is_preempted
>>>> +bool vcpu_is_preempted(int cpu);
>>>> +#endif
>>> Maybe paravirt.h is a better place?
>>
>> It is actually a little strange to add macro CONFIG_PARAVIRT in file
>> asm/spinlock.h
>>
>> vcpu_is_preempted is originally defined in header file
>> include/linux/sched.h like this
>> #ifndef vcpu_is_preempted
>> static inline bool vcpu_is_preempted(int cpu)
>> {
>> return false;
>> }
>> #endif
>>
>> that requires that header file is included before sched.h, file
>> asm/spinlock.h can meet this requirement, however header file paravirt.h
>> maybe it is not included before sched.h in generic.
>>
>> Here vcpu_is_preempted definition is added before the following including.
>> #include <asm/processor.h>
>> #include <asm/qspinlock.h>
>> #include <asm/qrwlock.h>
>> Maybe it is better to be added after the above header files including
>> sentences, but need further investigation.
> powerpc put it in paravirt.h, so I think it is possible.
paravirt.h is included by header file asm/qspinlock.h on powerpc,
however it is not so on loongarch :)
# grep paravirt.h arch/powerpc/* -r
arch/powerpc/include/asm/paravirt_api_clock.h:#include <asm/paravirt.h>
arch/powerpc/include/asm/qspinlock.h:#include <asm/paravirt.h>
arch/powerpc/include/asm/simple_spinlock.h:#include <asm/paravirt.h>
$ grep paravirt.h arch/loongarch/* -r
arch/loongarch/include/asm/paravirt_api_clock.h:#include <asm/paravirt.h>
>
>>>
>>>> +
>>>> #include <asm/processor.h>
>>>> #include <asm/qspinlock.h>
>>>> #include <asm/qrwlock.h>
>>>> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
>>>> index b1b51f920b23..b99404b6b13f 100644
>>>> --- a/arch/loongarch/kernel/paravirt.c
>>>> +++ b/arch/loongarch/kernel/paravirt.c
>>>> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
>>>> #ifdef CONFIG_SMP
>>>> static struct smp_ops native_ops;
>>>>
>>>> +static bool pv_vcpu_is_preempted(int cpu)
>>>> +{
>>>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>>>> +
>>>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
>>>> +}
>>>> +
>>>> static void pv_send_ipi_single(int cpu, unsigned int action)
>>>> {
>>>> int min, old;
>>>> @@ -308,6 +315,9 @@ int __init pv_time_init(void)
>>>> pr_err("Failed to install cpu hotplug callbacks\n");
>>>> return r;
>>>> }
>>>> +
>>>> + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
>>>> + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
>>>> #endif
>>>>
>>>> static_call_update(pv_steal_clock, paravt_steal_clock);
>>>> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
>>>>
>>>> return 0;
>>>> }
>>>> +
>>>> +bool notrace vcpu_is_preempted(int cpu)
>>>> +{
>>>> + return mp_ops.vcpu_is_preempted(cpu);
>>>> +}
>>>
>>> We can simplify the whole patch like this, then we don't need to touch
>>> smp.c, and we can merge Patch-2/3.
>>>
>>> +bool notrace vcpu_is_preempted(int cpu)
>>> +{
>>> + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
>>> + return false;
>>> + else {
>>> + struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
>>> + return !!(src->preempted & KVM_VCPU_PREEMPTED);
>>> + }
>>> +}
>> 1. there is assembly output about relative vcpu_is_preempted
>> <loongson_vcpu_is_preempted>:
>> move $r4,$r0
>> jirl $r0,$r1,0
>>
>> <pv_vcpu_is_preempted>:
>> pcalau12i $r13,8759(0x2237)
>> slli.d $r4,$r4,0x3
>> addi.d $r13,$r13,-1000(0xc18)
>> ldx.d $r13,$r13,$r4
>> pcalau12i $r12,5462(0x1556)
>> addi.d $r12,$r12,384(0x180)
>> add.d $r12,$r13,$r12
>> ld.bu $r4,$r12,16(0x10)
>> andi $r4,$r4,0x1
>> jirl $r0,$r1,0
>>
>> <vcpu_is_preempted>:
>> pcalau12i $r12,8775(0x2247)
>> ld.d $r12,$r12,-472(0xe28)
>> jirl $r0,$r12,0
>> andi $r0,$r0,0x0
>>
>> <vcpu_is_preempted_new>:
>> pcalau12i $r12,8151(0x1fd7)
>> ld.d $r12,$r12,-1008(0xc10)
>> bstrpick.d $r12,$r12,0x1a,0x1a
>> beqz $r12,188(0xbc) # 900000000024ec60
>> pcalau12i $r12,11802(0x2e1a)
>> addi.d $r12,$r12,-1400(0xa88)
>> ldptr.w $r14,$r12,36(0x24)
>> beqz $r14,108(0x6c) # 900000000024ec20
>> addi.w $r13,$r0,1(0x1)
>> bne $r14,$r13,164(0xa4) # 900000000024ec60
>> ldptr.w $r13,$r12,40(0x28)
>> bnez $r13,24(0x18) # 900000000024ebdc
>> lu12i.w $r14,262144(0x40000)
>> ori $r14,$r14,0x4
>> cpucfg $r14,$r14
>> slli.w $r13,$r14,0x0
>> st.w $r14,$r12,40(0x28)
>> bstrpick.d $r13,$r13,0x3,0x3
>> beqz $r13,128(0x80) # 900000000024ec60
>> pcalau12i $r13,8759(0x2237)
>> slli.d $r4,$r4,0x3
>> addi.d $r13,$r13,-1000(0xc18)
>> ldx.d $r13,$r13,$r4
>> pcalau12i $r12,5462(0x1556)
>> addi.d $r12,$r12,384(0x180)
>> add.d $r12,$r13,$r12
>> ld.bu $r4,$r12,16(0x10)
>> andi $r4,$r4,0x1
>> jirl $r0,$r1,0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> lu12i.w $r13,262144(0x40000)
>> cpucfg $r13,$r13
>> lu12i.w $r15,1237(0x4d5)
>> ori $r15,$r15,0x64b
>> slli.w $r13,$r13,0x0
>> bne $r13,$r15,-124(0x3ff84) # 900000000024ebb8
>> addi.w $r13,$r0,1(0x1)
>> st.w $r13,$r12,36(0x24)
>> b -128(0xfffff80) # 900000000024ebc0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> andi $r0,$r0,0x0
>> move $r4,$r0
>> jirl $r0,$r1,0
>>
>> With vcpu_is_preempted(), there is one memory load and one jirl jump,
>> with vcpu_is_preempted_new(), there is two memory load and two beq
>> compare instructions.
> Is vcpu_is_preempted() performance critical (we need performance data
> here)? It seems the powerpc version is also complex.
>
>>
>> 2. In some scenery such nr_cpus == 1, loongson_vcpu_is_preempted() is
>> better than pv_vcpu_is_preempted() even if the preempt feature is enabled.
> In your original patch, "mp_ops.vcpu_is_preempted =
> pv_vcpu_is_preempted" if the preempt feature is enabled. Why is
> loongson_vcpu_is_preempted() called when nr_cpus=1?
>
> Huacai
>
>>
>> Regards
>> Bibo Mao
>>> Huacai
>>>
>>>> +EXPORT_SYMBOL(vcpu_is_preempted);
>>>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
>>>> index 46036d98da75..f04192fedf8d 100644
>>>> --- a/arch/loongarch/kernel/smp.c
>>>> +++ b/arch/loongarch/kernel/smp.c
>>>> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
>>>> panic("IPI IRQ request failed\n");
>>>> }
>>>>
>>>> +static bool loongson_vcpu_is_preempted(int cpu)
>>>> +{
>>>> + return false;
>>>> +}
>>>> +
>>>> struct smp_ops mp_ops = {
>>>> .init_ipi = loongson_init_ipi,
>>>> .send_ipi_single = loongson_send_ipi_single,
>>>> .send_ipi_mask = loongson_send_ipi_mask,
>>>> + .vcpu_is_preempted = loongson_vcpu_is_preempted,
>>>> };
>>>>
>>>> static void __init fdt_smp_setup(void)
>>>> --
>>>> 2.39.3
>>>>
>>>>
>>
>>
© 2016 - 2025 Red Hat, Inc.