[v2] PREEMPT_AUTO: support lazy rescheduling

[PATCH v2 09/35] entry/kvm: handle lazy rescheduling at guest-entry

Posted by Ankur Arora 1 year, 8 months ago

Archs defining CONFIG_KVM_XFER_TO_GUEST_WORK call
xfer_to_guest_mode_handle_work() from various KVM vcpu-run
loops to check for any task work including rescheduling.

Handle TIF_NEED_RESCHED_LAZY alongside TIF_NEED_RESCHED.

Also, while at it, remove the explicit check for need_resched() in
the exit condition as that is already covered in the loop condition.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 include/linux/entry-kvm.h | 2 +-
 kernel/entry/kvm.c        | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
index 6813171afccb..674a622c91be 100644
--- a/include/linux/entry-kvm.h
+++ b/include/linux/entry-kvm.h
@@ -18,7 +18,7 @@
 
 #define XFER_TO_GUEST_MODE_WORK						\
 	(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL |	\
-	 _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
+	 _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED_LAZY | ARCH_XFER_TO_GUEST_MODE_WORK)
 
 struct kvm_vcpu;
 
diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c
index 2e0f75bcb7fd..8485f63863af 100644
--- a/kernel/entry/kvm.c
+++ b/kernel/entry/kvm.c
@@ -13,7 +13,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
 			return -EINTR;
 		}
 
-		if (ti_work & _TIF_NEED_RESCHED)
+		if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
 			schedule();
 
 		if (ti_work & _TIF_NOTIFY_RESUME)
@@ -24,7 +24,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
 			return ret;
 
 		ti_work = read_thread_flags();
-	} while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched());
+	} while (ti_work & XFER_TO_GUEST_MODE_WORK);
 	return 0;
 }
 
-- 
2.31.1

Re: [PATCH v2 09/35] entry/kvm: handle lazy rescheduling at guest-entry

Posted by Peter Zijlstra 1 year, 8 months ago

On Mon, May 27, 2024 at 05:34:55PM -0700, Ankur Arora wrote:
> Archs defining CONFIG_KVM_XFER_TO_GUEST_WORK call
> xfer_to_guest_mode_handle_work() from various KVM vcpu-run
> loops to check for any task work including rescheduling.
> 
> Handle TIF_NEED_RESCHED_LAZY alongside TIF_NEED_RESCHED.
> 
> Also, while at it, remove the explicit check for need_resched() in
> the exit condition as that is already covered in the loop condition.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Originally-by: Thomas Gleixner <tglx@linutronix.de>
> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
>  include/linux/entry-kvm.h | 2 +-
>  kernel/entry/kvm.c        | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
> index 6813171afccb..674a622c91be 100644
> --- a/include/linux/entry-kvm.h
> +++ b/include/linux/entry-kvm.h
> @@ -18,7 +18,7 @@
>  
>  #define XFER_TO_GUEST_MODE_WORK						\
>  	(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL |	\
> -	 _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
> +	 _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED_LAZY | ARCH_XFER_TO_GUEST_MODE_WORK)

Same as last patch, it seems weird to have both RESCHED flags so far
apart.

Re: [PATCH v2 09/35] entry/kvm: handle lazy rescheduling at guest-entry

Posted by Ankur Arora 1 year, 8 months ago

Peter Zijlstra <peterz@infradead.org> writes:

> On Mon, May 27, 2024 at 05:34:55PM -0700, Ankur Arora wrote:
>> Archs defining CONFIG_KVM_XFER_TO_GUEST_WORK call
>> xfer_to_guest_mode_handle_work() from various KVM vcpu-run
>> loops to check for any task work including rescheduling.
>>
>> Handle TIF_NEED_RESCHED_LAZY alongside TIF_NEED_RESCHED.
>>
>> Also, while at it, remove the explicit check for need_resched() in
>> the exit condition as that is already covered in the loop condition.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Originally-by: Thomas Gleixner <tglx@linutronix.de>
>> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>> ---
>>  include/linux/entry-kvm.h | 2 +-
>>  kernel/entry/kvm.c        | 4 ++--
>>  2 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
>> index 6813171afccb..674a622c91be 100644
>> --- a/include/linux/entry-kvm.h
>> +++ b/include/linux/entry-kvm.h
>> @@ -18,7 +18,7 @@
>>
>>  #define XFER_TO_GUEST_MODE_WORK						\
>>  	(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL |	\
>> -	 _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
>> +	 _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED_LAZY | ARCH_XFER_TO_GUEST_MODE_WORK)
>
> Same as last patch, it seems weird to have both RESCHED flags so far
> apart.

True. Will fix this and the other.

--
ankur