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

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Date:	Tue, 24 Apr 2012 19:12:27 +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 22:37 +0530, Srivatsa Vaddagiri wrote:
> * Peter Zijlstra <peterz@...radead.org> [2012-04-24 18:58:16]:
> 
> > 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?
> 
> The workload I am up against does experience tons of wakeup (after very short 
> (microsecond range) bursts of sleeps) and so am skeptical how the global 
> vruntime would keep up with this kind of workload. I'd be happy to test patches 
> and give feedback!

Thing is, global vruntime might fix that flaw/property you're exploiting
to get that preemption.


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