linux-kernel - Re: [PATCH 3/3] KVM: s390: clear kicked

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Date:   Wed, 20 Oct 2021 12:45:13 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Michael Mueller <mimu@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>, farman@...ux.ibm.com,
        kvm@...r.kernel.org, Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH 3/3] KVM: s390: clear kicked_mask if not idle after set

On Wed, 20 Oct 2021 12:31:19 +0200
Christian Borntraeger <borntraeger@...ibm.com> wrote:

> > Before releasing something like this, where none of us is sure if
> > it really saves cpu cost, I'd prefer to run some measurement with
> > the whole kicked_mask logic removed and to compare the number of
> > vcpu wake ups with the number of interrupts to be processed by
> > the gib alert mechanism in a slightly over committed host while
> > driving with Matthews test load.  
> 
> But I think patch 1 and 2 can go immediately as they measurably or
> testable fix things. Correct?

I think so as well. And if patch 3 is going to be dropped, I would
really like to keep the unconditional clear in kvm_arch_vcpu_runnable(),
as my analysis in the discussion points out: I think it can save us
form trouble this patch is trying to address.

Regards,
Halil