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

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Date: Thu, 30 May 2024 02:04:02 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, torvalds@...ux-foundation.org, paulmck@...nel.org,
        rostedt@...dmis.org, mark.rutland@....com, juri.lelli@...hat.com,
        joel@...lfernandes.org, raghavendra.kt@....com, sshegde@...ux.ibm.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Paolo Bonzini
 <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 09/35] entry/kvm: handle lazy rescheduling at
 guest-entry


Peter Zijlstra <peterz@...radead.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@...hat.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Originally-by: Thomas Gleixner <tglx@...utronix.de>
>> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
>> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.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