linux-kernel - Re: [PATCH][RSDL-mm 0/7] RSDL cpu scheduler for 2.6.21-rc3-mm2

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Date:	Tue, 13 Mar 2007 09:09:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mike Galbraith <efault@....de>, Con Kolivas <kernel@...ivas.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	ck list <ck@....kolivas.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH][RSDL-mm 0/7] RSDL cpu scheduler for 2.6.21-rc3-mm2

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > It has been said that "perfection is the enemy of good".  The two 
> > interactive tasks receiving 40% cpu while two niced background jobs 
> > receive 60% may well be perfect, but it's damn sure not good.
> 
> Well, the real problem is really "server that works on behalf of 
> somebody else".

i think Mike's testcase was even simpler than that: two plain CPU hogs 
on nice +5 stole much more CPU time with Con's new interactivity code 
than they did with the current interactivity code. I'd agree with Mike 
that a phenomenon like that needs to be fixed.

/less/ interactivity we can do easily in the current scheduler: just 
remove various bits here and there. The RSDL promise is that it gives us 
/more/ interactivity (with 'interactivity designed in', etc.), which in 
Mike's testcase does not seem to be the case.

> And the problem is that a lot of clients actually end up doing *more* 
> in the X server than they do themselves directly.

yeah. It's a hard case because X is not always a _clear_ interactive 
task - still the current interactivity code handles it quite well.

but Mike's scenario wasnt even that complex. It wasnt even a hard case 
of X being starved by _other_ interactive tasks running on the same nice 
level. Mike's test-scenario was about two plain nice +5 CPU hogs 
starving nice +0 interactive tasks more than the current scheduler does, 
and this is really not an area where we want to see any regression. Con, 
could you work on this area a bit more?

	Ingo
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