Date: Tue, 21 Mar 2006 15:25:04 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Con Kolivas <kernel@kolivas.org>
Cc: Mike Galbraith <efault@gmx.de>, Willy Tarreau <willy@w.ods.org>,
       lkml <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>,
       bugsplatter@gmail.com
Subject: Re: interactive task starvation
Message-ID: <20060321142504.GA31258@elte.hu>
References: <1142592375.7895.43.camel@homer> <200603220053.53595.kernel@kolivas.org> <1142950651.7807.95.camel@homer> <200603220119.50331.kernel@kolivas.org>
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* Con Kolivas <kernel@kolivas.org> wrote:

> On Wednesday 22 March 2006 01:17, Mike Galbraith wrote:
> > On Wed, 2006-03-22 at 00:53 +1100, Con Kolivas wrote:
> > > The yardstick for changes is now the speed of 'ls' scrolling in the
> > > console. Where exactly are those extra cycles going I wonder? Do you
> > > think the scheduler somehow makes the cpu idle doing nothing in that
> > > timespace? Clearly that's not true, and userspace is making something
> > > spin unnecessarily, but we're gonna fix that by modifying the
> > > scheduler.... sigh
> >
> > *Blink*
> >
> > Are you having a bad hair day??
> 
> My hair is approximately 3mm long so it's kinda hard for that to happen. 
> 
> What you're fixing with unfairness is worth pursuing. The 'ls' issue 
> just blows my mind though for reasons I've just said. Where are the 
> magic cycles going when nothing else is running that make it take ten 
> times longer?

i believe such artifacts are due to array switches not happening (due to 
the workload getting queued back to rq->active, not rq->expired), and 
'ls' only gets a timeslice once in a while, every STARVATION_LIMIT
times. I.e. such workloads penalize the CPU-bound 'ls' process quite 
heavily.

	Ingo
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