linux-kernel - Re: [PATCH v1] sched: steer waking task to empty cfs

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Date:	Tue, 24 Apr 2012 19:09:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] sched: steer waking task to empty cfs_rq for better
 latencies

On Tue, 2012-04-24 at 18:58 +0200, Peter Zijlstra wrote:
> On Tue, 2012-04-24 at 22:26 +0530, Srivatsa Vaddagiri wrote:
> > Steer a waking task towards a cpu where its cgroup has zero tasks (in
> > order to provide it better sleeper credits and hence reduce its wakeup
> > latency). 
> 
> That's just vile.. pjt could you post your global vruntime stuff so
> vatsa can have a go at that?

That is, you're playing a deficiency we should fix, not exploit.

Also, you do a second loop over all those cpus right after we've already
iterated them..

furthermore, that 100%+ gain is still way insane, what else is broken?
Did you try those paravirt tlb-flush patches and other such weirdness?
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