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

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Date:   Fri, 10 Nov 2017 15:12:55 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/swait: allow swake_up() to return

On Thu, Nov 09, 2017 at 11:06:53AM +0100, Paolo Bonzini wrote:
> On 09/11/2017 10:18, Peter Xu wrote:
> > Let swake_up() to return whether any of the waiters is waked up. One use
> > case of it would be:
> > 
> >   if (swait_active(wq)) {
> >     swake_up(wq);
> >     // do something when waiter is waked up
> >     waked_up++;
> >   }
> > 
> > Logically it's possible that when reaching swake_up() the wait queue is
> > not active any more, and here doing something like waked_up++ would be
> > inaccurate.  To correct it, we need an atomic version of it.
> > 
> > With this patch, we can simply re-write it into:
> > 
> >   if (swake_up(wq)) {
> >     // do something when waiter is waked up
> >     waked_up++;
> >   }
> > 
> > After all we are checking swait_active() inside swake_up() too.
> 
> Better subject:
> 
> sched/swait: make swake_up() return whether there were any waiters
> 
> I like this patch.

I'll see how PeterZ would like me to do next, or I can drop this patch
and send another clean up which is part of patch 2.  Thanks for the
positive feedback and commenting. :-)

-- 
Peter Xu