From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Willy Tarreau <willy@w.ods.org>
Subject: Re: interactive task starvation
Date: Tue, 21 Mar 2006 19:39:11 +0100
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Cc: Con Kolivas <kernel@kolivas.org>, Mike Galbraith <efault@gmx.de>,
       Ingo Molnar <mingo@elte.hu>, lkml <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, bugsplatter@gmail.com
References: <1142592375.7895.43.camel@homer> <200603220119.50331.kernel@kolivas.org> <20060321143941.GD26171@w.ods.org>
In-Reply-To: <20060321143941.GD26171@w.ods.org>
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On Tuesday 21 March 2006 15:39, Willy Tarreau wrote:
> On Wed, Mar 22, 2006 at 01:19:49AM +1100, Con Kolivas 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?
> 
> Con, those cycles are not "magic", if you look at the numbers, the time is
> not spent in the process itself. From what has been observed since the
> beginning, it is spent :
>   - in other processes which are starvating the CPU (eg: X11 when xterm
>     scrolls)
>   - in context switches when you have a pipe somewhere and the CPU is
>     bouncing between tasks.
> 
> Concerning your angriness about me being OK with (0,0) and still
> asking for tunables, it's precisely because I know that *my* workload
> is not everyone else's, and I don't want to conclude too quickly that
> there are only two types of workloads.

Well, perhaps we can assume there are only two types of workloads and
wait for a test case that will show the assumption is wrong?

> Maybe you're right, maybe you're wrong. At least you're right for as long
> as no other workload has been identified. But thinking like this is like
> some time ago when we thought that "if it runs XMMS without skipping,
> it'll be OK for everyone".

However, we should not try to anticipate every possible kind of workload
IMHO.

Greetings,
Rafael
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