Subject: Re: [git pull] scheduler fixes
From: Mike Galbraith <efault@gmx.de>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <20090117161222.GC31601@elte.hu>
References: <20090111144305.GA7154@elte.hu>
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	 <1232173776.7073.21.camel@marge.simson.net>
	 <1232186054.6813.48.camel@marge.simson.net>
	 <20090117161222.GC31601@elte.hu>
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Date: Sat, 17 Jan 2009 17:28:47 +0100
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On Sat, 2009-01-17 at 17:12 +0100, Ingo Molnar wrote:
> * Mike Galbraith <efault@gmx.de> wrote:
> 
> > Dunno about the IO bits, but..
> >  
> > The problem with the C++ testcases seems to be wake_up_all() plunking a 
> > genuine thundering herd onto runqueues.  The sleeper fairness logic 
> > places the entire herd left of min_vruntime, meaning N*sched_latency 
> > pain for the poor sods who are setting the runqueue pace.
> 
> 100 wakeup pairs that all run and ping-pong between each other?
> 
> That creates 200 tasks with an average system load of 100.0, on a 
> dual-core system. Is that a fair representation of some real workload, or 
> just an unrealistic "gee, look, given enough tasks running I can overload 
> the system _this bad_" example?

Looks contrived to me, but it is a hole.  Dang sleepers, can't live with
'em can't live without 'em.

	-Mike

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