Subject: Re: [RFC -v2 PATCH 2/3] sched: add yield_to function
From: Mike Galbraith <efault@gmx.de>
To: Avi Kivity <avi@redhat.com>
Cc: Rik van Riel <riel@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Chris Wright <chrisw@sous-sol.org>
In-Reply-To: <4D0F3266.90908@redhat.com>
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	 <1292569018.7772.75.camel@marge.simson.net>  <4D0B7D24.5060207@redhat.com>
	 <1292615509.7381.81.camel@marge.simson.net>  <4D0CE937.8090601@redhat.com>
	 <1292699204.1181.51.camel@marge.simson.net>  <4D0DA45A.9070600@redhat.com>
	 <1292753156.16367.104.camel@marge.simson.net> <4D0DCE10.7000200@redhat.com>
	 <1292834372.8948.27.camel@marge.simson.net> <4D0F1794.3010803@redhat.com>
	 <1292835302.8948.35.camel@marge.simson.net> <4D0F1BD8.20601@redhat.com>
	 <1292837440.8948.60.camel@marge.simson.net> <4D0F25E8.80305@redhat.com>
	 <1292841193.11946.36.camel@marge.simson.net>  <4D0F3266.90908@redhat.com>
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Date: Mon, 20 Dec 2010 11:46:50 +0100
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On Mon, 2010-12-20 at 12:39 +0200, Avi Kivity wrote:
> On 12/20/2010 12:33 PM, Mike Galbraith wrote:
> > >
> > >  Correct.  I don't want the other task to run before me, I just don't
> > >  want to run before it.
> >
> > OK, so what I gather is that if you can preempt another of your own
> > threads to get the target to cpu, that would be a good thing whether
> > he's on the same cpu as yield_to() caller or not.  If the target is
> > sharing a cpu with you, that's even better.  Correct?
> 
> Correct.  I'm not interested in scheduling wrt other tasks, just my tasks.
> 
> However, if I'm all alone on my cpu, and the other task is runnable but 
> not running, behind some unrelated task, then I do need that task to be 
> preempted (or to move tasks around).

So in that case, a pull may be advantageous.

> > Would a kick/hint option be useful?
> 
> Depends on what it does...

Let you decide whether you only want to drop a hint and leave it at
that, or also attempt a preemption.

	-Mike


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