linux-kernel - Re: [PATCH 1/2] sched/swait: allow swake

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Message-ID: <20171113051948.GB7603@xz-mi>
Date:   Mon, 13 Nov 2017 13:19:48 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Kr??m???? <rkrcmar@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/swait: allow swake_up() to return

On Mon, Nov 13, 2017 at 11:33:43AM +0800, Peter Xu wrote:
> On Fri, Nov 10, 2017 at 09:05:20AM +0100, Peter Zijlstra wrote:
> > On Fri, Nov 10, 2017 at 03:10:17PM +0800, Peter Xu wrote:
> > > I came to this when reading kvm_vcpu_wake_up(), so that only affects
> > > some statistic which may not be that critical.  However I don't know
> > > whether there would be any other real use case that we would like to
> > > know exactly whether a call to [s]wake_up() has really done something
> > > or just returned with a NOP.
> > > 
> > > Anyway, please let me know if you think the same change to wake_up()
> > > would be meaningful, otherwise I can drop this patch and post another
> > > KVM-only one to clean up the redundant callers of swait_active(),
> > > since even if we dropped that list check in 35a2897c2a30, we'll do
> > > that again in swake_up_locked().
> > 
> > See commits:
> > 
> >   8cd641e3c7cb ("sched/wait: Add swq_has_sleeper()")
> >   5e0018b3e39e ("kvm: Serialize wq active checks in kvm_vcpu_wake_up()")
> > 
> > 
> > In any case, I don't think we want the change you propose. The numbers
> > don't mean much and there's no point in making all the callers in the
> > kernel slower for it.
> 
> I see. And also we can introduce a new API for that if really needed.
> 
> I'll repost with KVM only changes.  Thanks for reviewing.

Wait... I see that https://lkml.org/lkml/2017/9/5/622 seems to have
fixed all the occurences.  So I'll drop the series.  Thanks,

-- 
Peter Xu