Re: interactive task starvation

[Con Kolivas <kernel@kolivas.org>]

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