linux-kernel - Re: [PATCH 4/5] kvm: Replace vcpu->swait with rcuwait

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Message-ID: <20200423091911.GP20730@hirez.programming.kicks-ass.net>
Date:   Thu, 23 Apr 2020 11:19:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Marc Zyngier <maz@...nel.org>, Davidlohr Bueso <dave@...olabs.net>,
        tglx@...utronix.de, kvm@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>,
        torvalds@...ux-foundation.org, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        linux-mips@...r.kernel.org, Paul Mackerras <paulus@...abs.org>,
        joel@...lfernandes.org, will@...nel.org,
        kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH 4/5] kvm: Replace vcpu->swait with rcuwait

On Thu, Apr 23, 2020 at 10:57:57AM +0200, Paolo Bonzini wrote:
> On 23/04/20 10:41, Marc Zyngier wrote:
> >>  
> >> -	if (swait_active(kvm_arch_vcpu_wq(vcpu)))
> >> +	if (rcu_dereference(kvm_arch_vpu_get_wait(vcpu)) != NULL)
> > This doesn't compile (wrong function name, and rcu_dereference takes a
> > variable). But whatever it would do if we fixed it looks dodgy. it isn't
> > the rcuwait structure that you want to dereference, but rcuwait->task
> > (we are checking whether we are called because we are blocking or being
> > preempted).
> > 
> 
> Yes, I agree.  Replacing swait with rcuwait is all good, but please make
> the API look the same first.  Just like you added prepare_to_rcuwait and
> finish_rcuwait, let's add rcuwait_active as well.
> 
> Actually let's do it like this:
> 
> 1) Davidlohr, please post only patches 1-3 to "equalize" the swait and
> rcuwait APIs.
> 
> 2) Peter, please prepare a topic branch for those, or provide Acked-by

I don't think I have anything that conflicts with this, so sure, take
the whole thing through KVM.

For 1-3 (and I'll send a small niggle for 3 right after this):

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

I'll keep 5 as it is unrelated.