From: Con Kolivas <kernel@kolivas.org>
To: Mike Galbraith <efault@gmx.de>
Subject: Re: interactive task starvation
Date: Wed, 22 Mar 2006 00:13:15 +1100
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Cc: Ingo Molnar <mingo@elte.hu>, Willy Tarreau <willy@w.ods.org>,
       lkml <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>,
       bugsplatter@gmail.com
References: <200603090036.49915.kernel@kolivas.org> <200603212253.03637.kernel@kolivas.org> <1142946610.7807.43.camel@homer>
In-Reply-To: <1142946610.7807.43.camel@homer>
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On Wednesday 22 March 2006 00:10, Mike Galbraith wrote:
> On Tue, 2006-03-21 at 22:53 +1100, Con Kolivas wrote:
> > On Tuesday 21 March 2006 22:18, Ingo Molnar wrote:
> > > great work by Mike! One detail: i'd like there to be just one default
> > > throttling value, i.e. no grace_g tunables [so that we have just one
> > > default scheduler behavior]. Is the default grace_g[12] setting good
> > > enough for your workload?
> >
> > I agree. If anything is required, a simple on/off tunable makes much more
> > sense. Much like I suggested ages ago with an "interactive" switch which
> > was rather unpopular when I first suggested it.
>
> Let me try to explain why on/off is not sufficient.
>
> You notice how Willy said that his notebook is more responsive with
> tunables set to 0,0?  That's important, because it's absolutely true...
> depending what you're doing.  Setting tunables to 0,0 cuts off the idle
> sleep logic, and the sleep_avg divisor - both of which were put there
> specifically for interactivity - and returns the scheduler to more or
> less original O(1) scheduler.  You and I both know that these are most
> definitely needed in a Desktop environment.  For instance, if Willy
> starts editing code in X, and scrolls while something is running in the
> background, he'll suddenly say hey, maybe this _ain't_ more responsive,
> because all of a sudden the starvation added with the interactivity
> logic will be sorely missed as my throttle wrings X's neck.
>
> How long should Willy be able to scroll without feeling the background,
> and how long should Apache be able to starve his shell.  They are one
> and the same, and I can't say, because I'm not Willy.  I don't know how
> to get there from here without tunables.  Picking defaults is one thing,
> but I don't know how to make it one-size-fits-all.  For the general
> case, the values delivered will work fine.  For the apache case, they
> absolutely 100% guaranteed will not.

So how do you propose we tune such a beast then? Apache users will use off, 
everyone else will have no idea but to use the defaults.

Cheers,
Con
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