powerpc: Enable lazy preemption

[PATCH v2 1/2] powerpc: Add preempt lazy support

Posted by Shrikanth Hegde 1 year, 2 months ago

Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
16 bit range of NEED_RESCHED, so compiler can issue single andi.

Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
return to kernel.

Ran a few benchmarks and db workload on Power10. Performance is close to
preempt=none/voluntary.
 
Since Powerpc systems can have large core count and large memory,
preempt lazy is going to be helpful in avoiding soft lockup issues.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 arch/powerpc/Kconfig                   | 1 +
 arch/powerpc/include/asm/thread_info.h | 9 ++++++---
 arch/powerpc/kernel/interrupt.c        | 4 ++--
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 8094a01974cc..2f625aecf94b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -145,6 +145,7 @@ config PPC
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PHYS_TO_DMA
 	select ARCH_HAS_PMEM_API
+	select ARCH_HAS_PREEMPT_LAZY
 	select ARCH_HAS_PTE_DEVMAP		if PPC_BOOK3S_64
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SCALED_CPUTIME		if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 6ebca2996f18..2785c7462ebf 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -103,6 +103,7 @@ void arch_setup_new_exec(void);
 #define TIF_PATCH_PENDING	6	/* pending live patching update */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SINGLESTEP		8	/* singlestepping active */
+#define TIF_NEED_RESCHED_LAZY	9       /* Scheduler driven lazy preemption */
 #define TIF_SECCOMP		10	/* secure computing */
 #define TIF_RESTOREALL		11	/* Restore all regs (implies NOERROR) */
 #define TIF_NOERROR		12	/* Force successful syscall return */
@@ -122,6 +123,7 @@ void arch_setup_new_exec(void);
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
+#define _TIF_NEED_RESCHED_LAZY	(1<<TIF_NEED_RESCHED_LAZY)
 #define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1<<TIF_32BIT)
@@ -142,9 +144,10 @@ void arch_setup_new_exec(void);
 				 _TIF_SYSCALL_EMU)
 
 #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
-				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
-				 _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \
-				 _TIF_NOTIFY_SIGNAL)
+				 _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \
+				 _TIF_UPROBE | _TIF_RESTORE_TM | \
+				 _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL)
+
 #define _TIF_PERSYSCALL_MASK	(_TIF_RESTOREALL|_TIF_NOERROR)
 
 /* Bits in local_flags */
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index af62ec974b97..8f4acc55407b 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
 	ti_flags = read_thread_flags();
 	while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
 		local_irq_enable();
-		if (ti_flags & _TIF_NEED_RESCHED) {
+		if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
 			schedule();
 		} else {
 			/*
@@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 		/* Returning to a kernel context with local irqs enabled. */
 		WARN_ON_ONCE(!(regs->msr & MSR_EE));
 again:
-		if (IS_ENABLED(CONFIG_PREEMPT)) {
+		if (IS_ENABLED(CONFIG_PREEMPTION)) {
 			/* Return to preemptible kernel context */
 			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
 				if (preempt_count() == 0)
-- 
2.43.5

Re: [PATCH v2 1/2] powerpc: Add preempt lazy support

Posted by Christophe Leroy 1 year, 2 months ago


Le 16/11/2024 à 20:23, Shrikanth Hegde a écrit :
> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
> 
> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
> return to kernel.

FWIW, there is work in progress on using generic entry/exit for powerpc, 
if you can help testing it that can help, see 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/F0AE0A4571CE3126+20241111031934.1579-2-luming.yu@shingroup.cn/

Christophe


> 
> Ran a few benchmarks and db workload on Power10. Performance is close to
> preempt=none/voluntary.
>   
> Since Powerpc systems can have large core count and large memory,
> preempt lazy is going to be helpful in avoiding soft lockup issues.
> 
> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Reviewed-by: Ankur Arora <ankur.a.arora@oracle.com>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>   arch/powerpc/Kconfig                   | 1 +
>   arch/powerpc/include/asm/thread_info.h | 9 ++++++---
>   arch/powerpc/kernel/interrupt.c        | 4 ++--
>   3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 8094a01974cc..2f625aecf94b 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -145,6 +145,7 @@ config PPC
>   	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>   	select ARCH_HAS_PHYS_TO_DMA
>   	select ARCH_HAS_PMEM_API
> +	select ARCH_HAS_PREEMPT_LAZY
>   	select ARCH_HAS_PTE_DEVMAP		if PPC_BOOK3S_64
>   	select ARCH_HAS_PTE_SPECIAL
>   	select ARCH_HAS_SCALED_CPUTIME		if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index 6ebca2996f18..2785c7462ebf 100644
> --- a/arch/powerpc/include/asm/thread_info.h
> +++ b/arch/powerpc/include/asm/thread_info.h
> @@ -103,6 +103,7 @@ void arch_setup_new_exec(void);
>   #define TIF_PATCH_PENDING	6	/* pending live patching update */
>   #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
>   #define TIF_SINGLESTEP		8	/* singlestepping active */
> +#define TIF_NEED_RESCHED_LAZY	9       /* Scheduler driven lazy preemption */
>   #define TIF_SECCOMP		10	/* secure computing */
>   #define TIF_RESTOREALL		11	/* Restore all regs (implies NOERROR) */
>   #define TIF_NOERROR		12	/* Force successful syscall return */
> @@ -122,6 +123,7 @@ void arch_setup_new_exec(void);
>   #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>   #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
>   #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
> +#define _TIF_NEED_RESCHED_LAZY	(1<<TIF_NEED_RESCHED_LAZY)
>   #define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
>   #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
>   #define _TIF_32BIT		(1<<TIF_32BIT)
> @@ -142,9 +144,10 @@ void arch_setup_new_exec(void);
>   				 _TIF_SYSCALL_EMU)
>   
>   #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
> -				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
> -				 _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \
> -				 _TIF_NOTIFY_SIGNAL)
> +				 _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \
> +				 _TIF_UPROBE | _TIF_RESTORE_TM | \
> +				 _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL)
> +
>   #define _TIF_PERSYSCALL_MASK	(_TIF_RESTOREALL|_TIF_NOERROR)
>   
>   /* Bits in local_flags */
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index af62ec974b97..8f4acc55407b 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
>   	ti_flags = read_thread_flags();
>   	while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
>   		local_irq_enable();
> -		if (ti_flags & _TIF_NEED_RESCHED) {
> +		if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
>   			schedule();
>   		} else {
>   			/*
> @@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
>   		/* Returning to a kernel context with local irqs enabled. */
>   		WARN_ON_ONCE(!(regs->msr & MSR_EE));
>   again:
> -		if (IS_ENABLED(CONFIG_PREEMPT)) {
> +		if (IS_ENABLED(CONFIG_PREEMPTION)) {
>   			/* Return to preemptible kernel context */
>   			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
>   				if (preempt_count() == 0)

Re: [PATCH v2 1/2] powerpc: Add preempt lazy support

Posted by Shrikanth Hegde 1 year, 2 months ago


On 11/26/24 16:23, Christophe Leroy wrote:
> 
> 
> Le 16/11/2024 à 20:23, Shrikanth Hegde a écrit :
>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>
>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>> return to kernel.
> 
> FWIW, there is work in progress on using generic entry/exit for powerpc, 
> if you can help testing it that can help, see https:// 
> patchwork.ozlabs.org/project/linuxppc-dev/patch/ 
> F0AE0A4571CE3126+20241111031934.1579-2-luming.yu@shingroup.cn/
>

I gave that series a try. After a lot of manual patching on tip tree and 
removal of multiple definition of regs_irqs_disabled, i was able to 
compile and boot.

I am skimming through the series, but as far as i understand from the 
comments, it needs to be redesigned. I probably get it why. I will go 
through it in more detail to figure out how to do it better. I believe 
the changes have to stem from interrupt_64.S

As far as the bits of this patch with that patch concerned, it is with 
NEED_RESCHED bits. There atleast couple of major issues in that patch 
series that are wrong.

1. It only tries to move exit to user to generic. exit to kernel is not. 
there is generic irqentry_exit that handles it for generic code. powerpc 
exit to kernel still there.

2. Even for exit to user, it ends up calling exit_to_user_mode_loop 
twice for the same syscall. that seems wrong. once in 
interrupt_exit_user_prepare_main and once through 
syscall_exit_to_user_mode in syscall_exit_prepare.


> Christophe
> 

So I guess, when we do eventually if move, this checks would be removed 
at that point along with rest of the code.

> 
>>
>> Ran a few benchmarks and db workload on Power10. Performance is close to
>> preempt=none/voluntary.
>> Since Powerpc systems can have large core count and large memory,
>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>
>> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Reviewed-by: Ankur Arora <ankur.a.arora@oracle.com>
>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>> ---
>>   arch/powerpc/Kconfig                   | 1 +
>>   arch/powerpc/include/asm/thread_info.h | 9 ++++++---
>>   arch/powerpc/kernel/interrupt.c        | 4 ++--
>>   3 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 8094a01974cc..2f625aecf94b 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -145,6 +145,7 @@ config PPC
>>       select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>>       select ARCH_HAS_PHYS_TO_DMA
>>       select ARCH_HAS_PMEM_API
>> +    select ARCH_HAS_PREEMPT_LAZY
>>       select ARCH_HAS_PTE_DEVMAP        if PPC_BOOK3S_64
>>       select ARCH_HAS_PTE_SPECIAL
>>       select ARCH_HAS_SCALED_CPUTIME        if 
>> VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
>> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/ 
>> include/asm/thread_info.h
>> index 6ebca2996f18..2785c7462ebf 100644
>> --- a/arch/powerpc/include/asm/thread_info.h
>> +++ b/arch/powerpc/include/asm/thread_info.h
>> @@ -103,6 +103,7 @@ void arch_setup_new_exec(void);
>>   #define TIF_PATCH_PENDING    6    /* pending live patching update */
>>   #define TIF_SYSCALL_AUDIT    7    /* syscall auditing active */
>>   #define TIF_SINGLESTEP        8    /* singlestepping active */
>> +#define TIF_NEED_RESCHED_LAZY    9       /* Scheduler driven lazy 
>> preemption */
>>   #define TIF_SECCOMP        10    /* secure computing */
>>   #define TIF_RESTOREALL        11    /* Restore all regs (implies 
>> NOERROR) */
>>   #define TIF_NOERROR        12    /* Force successful syscall return */
>> @@ -122,6 +123,7 @@ void arch_setup_new_exec(void);
>>   #define _TIF_SYSCALL_TRACE    (1<<TIF_SYSCALL_TRACE)
>>   #define _TIF_SIGPENDING        (1<<TIF_SIGPENDING)
>>   #define _TIF_NEED_RESCHED    (1<<TIF_NEED_RESCHED)
>> +#define _TIF_NEED_RESCHED_LAZY    (1<<TIF_NEED_RESCHED_LAZY)
>>   #define _TIF_NOTIFY_SIGNAL    (1<<TIF_NOTIFY_SIGNAL)
>>   #define _TIF_POLLING_NRFLAG    (1<<TIF_POLLING_NRFLAG)
>>   #define _TIF_32BIT        (1<<TIF_32BIT)
>> @@ -142,9 +144,10 @@ void arch_setup_new_exec(void);
>>                    _TIF_SYSCALL_EMU)
>>   #define _TIF_USER_WORK_MASK    (_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
>> -                 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
>> -                 _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \
>> -                 _TIF_NOTIFY_SIGNAL)
>> +                 _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \
>> +                 _TIF_UPROBE | _TIF_RESTORE_TM | \
>> +                 _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL)
>> +
>>   #define _TIF_PERSYSCALL_MASK    (_TIF_RESTOREALL|_TIF_NOERROR)
>>   /* Bits in local_flags */
>> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/ 
>> interrupt.c
>> index af62ec974b97..8f4acc55407b 100644
>> --- a/arch/powerpc/kernel/interrupt.c
>> +++ b/arch/powerpc/kernel/interrupt.c
>> @@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long 
>> ret, struct pt_regs *regs)
>>       ti_flags = read_thread_flags();
>>       while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & 
>> ~_TIF_RESTORE_TM))) {
>>           local_irq_enable();
>> -        if (ti_flags & _TIF_NEED_RESCHED) {



>> +        if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
>>               schedule();
>>           } else {
>>               /*
>> @@ -396,7 +396,7 @@ notrace unsigned long 
>> interrupt_exit_kernel_prepare(struct pt_regs *regs)
>>           /* Returning to a kernel context with local irqs enabled. */
>>           WARN_ON_ONCE(!(regs->msr & MSR_EE));
>>   again:
>> -        if (IS_ENABLED(CONFIG_PREEMPT)) {
>> +        if (IS_ENABLED(CONFIG_PREEMPTION)) {
>>               /* Return to preemptible kernel context */
>>               if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
>>                   if (preempt_count() == 0)

Re: [PATCH v2 1/2] powerpc: Add preempt lazy support

Posted by Luming Yu 1 year, 1 month ago

On Mon, Dec 02, 2024 at 12:58:59AM +0530, Shrikanth Hegde wrote:
> 
> 
> On 11/26/24 16:23, Christophe Leroy wrote:
> > 
> > 
> > Le 16/11/2024 à 20:23, Shrikanth Hegde a écrit :
> > > Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
> > > 16 bit range of NEED_RESCHED, so compiler can issue single andi.
> > > 
> > > Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
> > > to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
> > > return to kernel.
> > 
> > FWIW, there is work in progress on using generic entry/exit for powerpc,
> > if you can help testing it that can help, see https://
> > patchwork.ozlabs.org/project/linuxppc-dev/patch/
> > F0AE0A4571CE3126+20241111031934.1579-2-luming.yu@shingroup.cn/
> > 
> 
> I gave that series a try. After a lot of manual patching on tip tree and
> removal of multiple definition of regs_irqs_disabled, i was able to compile
> and boot.
> 
> I am skimming through the series, but as far as i understand from the
> comments, it needs to be redesigned. I probably get it why. I will go
> through it in more detail to figure out how to do it better. I believe the
> changes have to stem from interrupt_64.S

Thanks for your time for the work.

when you do it, besides compile, boot, and ppc linux-ci github workflow, 
please also do selftest 
make -C tools/testing/selftest TARGETS=seccomp run_tests to make sure
all secommp 98 unit tests passed. 

> 
> As far as the bits of this patch with that patch concerned, it is with
> NEED_RESCHED bits. There atleast couple of major issues in that patch series
> that are wrong.
> 
> 1. It only tries to move exit to user to generic. exit to kernel is not.
> there is generic irqentry_exit that handles it for generic code. powerpc
> exit to kernel still there.
> 
> 2. Even for exit to user, it ends up calling exit_to_user_mode_loop twice
> for the same syscall. that seems wrong. once in
> interrupt_exit_user_prepare_main and once through syscall_exit_to_user_mode
> in syscall_exit_prepare.

I knew this as ppc system call uses interrupt path. I planned to delete
ppc speicifc interrupt_exit_user_prepare_main later for this series.

Now it might be good timing to complete it as there is a real use case need this
to be done. :-)
    
> 
> 
> > Christophe
> > 
> 
> So I guess, when we do eventually if move, this checks would be removed at
> that point along with rest of the code.
> 
> > 
> > > 
> > > Ran a few benchmarks and db workload on Power10. Performance is close to
> > > preempt=none/voluntary.
> > > Since Powerpc systems can have large core count and large memory,
> > > preempt lazy is going to be helpful in avoiding soft lockup issues.
> > > 
> > > Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > > Reviewed-by: Ankur Arora <ankur.a.arora@oracle.com>
> > > Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> > > ---
> > >   arch/powerpc/Kconfig                   | 1 +
> > >   arch/powerpc/include/asm/thread_info.h | 9 ++++++---
> > >   arch/powerpc/kernel/interrupt.c        | 4 ++--
> > >   3 files changed, 9 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > > index 8094a01974cc..2f625aecf94b 100644
> > > --- a/arch/powerpc/Kconfig
> > > +++ b/arch/powerpc/Kconfig
> > > @@ -145,6 +145,7 @@ config PPC
> > >       select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> > >       select ARCH_HAS_PHYS_TO_DMA
> > >       select ARCH_HAS_PMEM_API
> > > +    select ARCH_HAS_PREEMPT_LAZY
> > >       select ARCH_HAS_PTE_DEVMAP        if PPC_BOOK3S_64
> > >       select ARCH_HAS_PTE_SPECIAL
> > >       select ARCH_HAS_SCALED_CPUTIME        if
> > > VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
> > > diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/
> > > include/asm/thread_info.h
> > > index 6ebca2996f18..2785c7462ebf 100644
> > > --- a/arch/powerpc/include/asm/thread_info.h
> > > +++ b/arch/powerpc/include/asm/thread_info.h
> > > @@ -103,6 +103,7 @@ void arch_setup_new_exec(void);
> > >   #define TIF_PATCH_PENDING    6    /* pending live patching update */
> > >   #define TIF_SYSCALL_AUDIT    7    /* syscall auditing active */
> > >   #define TIF_SINGLESTEP        8    /* singlestepping active */
> > > +#define TIF_NEED_RESCHED_LAZY    9       /* Scheduler driven lazy
> > > preemption */
> > >   #define TIF_SECCOMP        10    /* secure computing */
> > >   #define TIF_RESTOREALL        11    /* Restore all regs (implies
> > > NOERROR) */
> > >   #define TIF_NOERROR        12    /* Force successful syscall return */
> > > @@ -122,6 +123,7 @@ void arch_setup_new_exec(void);
> > >   #define _TIF_SYSCALL_TRACE    (1<<TIF_SYSCALL_TRACE)
> > >   #define _TIF_SIGPENDING        (1<<TIF_SIGPENDING)
> > >   #define _TIF_NEED_RESCHED    (1<<TIF_NEED_RESCHED)
> > > +#define _TIF_NEED_RESCHED_LAZY    (1<<TIF_NEED_RESCHED_LAZY)
> > >   #define _TIF_NOTIFY_SIGNAL    (1<<TIF_NOTIFY_SIGNAL)
> > >   #define _TIF_POLLING_NRFLAG    (1<<TIF_POLLING_NRFLAG)
> > >   #define _TIF_32BIT        (1<<TIF_32BIT)
> > > @@ -142,9 +144,10 @@ void arch_setup_new_exec(void);
> > >                    _TIF_SYSCALL_EMU)
> > >   #define _TIF_USER_WORK_MASK    (_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
> > > -                 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
> > > -                 _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \
> > > -                 _TIF_NOTIFY_SIGNAL)
> > > +                 _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \
> > > +                 _TIF_UPROBE | _TIF_RESTORE_TM | \
> > > +                 _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL)
> > > +
> > >   #define _TIF_PERSYSCALL_MASK    (_TIF_RESTOREALL|_TIF_NOERROR)
> > >   /* Bits in local_flags */
> > > diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/
> > > interrupt.c
> > > index af62ec974b97..8f4acc55407b 100644
> > > --- a/arch/powerpc/kernel/interrupt.c
> > > +++ b/arch/powerpc/kernel/interrupt.c
> > > @@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long
> > > ret, struct pt_regs *regs)
> > >       ti_flags = read_thread_flags();
> > >       while (unlikely(ti_flags & (_TIF_USER_WORK_MASK &
> > > ~_TIF_RESTORE_TM))) {
> > >           local_irq_enable();
> > > -        if (ti_flags & _TIF_NEED_RESCHED) {
> 
> 
> 
> > > +        if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
> > >               schedule();
> > >           } else {
> > >               /*
> > > @@ -396,7 +396,7 @@ notrace unsigned long
> > > interrupt_exit_kernel_prepare(struct pt_regs *regs)
> > >           /* Returning to a kernel context with local irqs enabled. */
> > >           WARN_ON_ONCE(!(regs->msr & MSR_EE));
> > >   again:
> > > -        if (IS_ENABLED(CONFIG_PREEMPT)) {
> > > +        if (IS_ENABLED(CONFIG_PREEMPTION)) {
> > >               /* Return to preemptible kernel context */
> > >               if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
> > >                   if (preempt_count() == 0)
>

[PATCH v2 1/2] powerpc: Add preempt lazy support
[PATCH v2 2/2] powerpc: Large user copy aware of full:rt:lazy preemption