linux-kernel - Re: [PATCH v3 2/4] KVM: use simple waitqueue for vcpu->wq

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Message-ID: <20151020160609.GH17308@twins.programming.kicks-ass.net>
Date:	Tue, 20 Oct 2015 18:06:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Daniel Wagner <daniel.wagner@...-carit.de>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 2/4] KVM: use simple waitqueue for vcpu->wq

On Tue, Oct 20, 2015 at 05:40:36PM +0200, Paolo Bonzini wrote:
> 
> 
> On 20/10/2015 16:00, Peter Zijlstra wrote:
> >> > -		prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
> >> > +		prepare_to_swait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
> >> >  
> >> >  		if (kvm_vcpu_check_block(vcpu) < 0)
> >> >  			break;
> >> > @@ -2028,7 +2027,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> >> >  		schedule();
> >> >  	}
> >> >  
> >> > -	finish_wait(&vcpu->wq, &wait);
> >> > +	finish_swait(&vcpu->wq, &wait);
> >> >  	cur = ktime_get();
> >> >  
> >> >  out:
> > Should we not take this opportunity to get rid of these open-coded wait
> > loops?
> 
> I find them way more readable than a 6-argument __wait_event...

I could introduce wait_event_idle_cmd() and be at 3 if you think that
helps.

#define __wait_event_idle_cmd(wq, cond, cmd) \
	___wait_event(wq, cond, TASK_IDLE, 0, 0, cmd)

etc..

Its that awkward waited variable that makes it hard to use the 'regular'
2 parameter thing. Although you could of course do horrible things like:

	__wait_event_idle(vcpu->wq, ({
		bool done = kvm_cpu_check_block(vcpu) < 0;
		if (!done)
			waited = true;
		done;
	}));

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