linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Message-ID: <20070414083625.GM943@1wt.eu>
Date:	Sat, 14 Apr 2007 10:36:25 +0200
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

On Sat, Apr 14, 2007 at 10:08:34AM +0200, Willy Tarreau wrote:
> On Sat, Apr 14, 2007 at 08:43:34AM +0200, Ingo Molnar wrote:
> > 
> > * Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > Nick noticed that upon fork we change parent->wait_runtime but we do 
> > > not requeue it within the rbtree.
> > 
> > this fix is not complete - because the child runqueue is locked here, 
> > not the parent's. I've fixed this properly in my tree and have uploaded 
> > a new sched-modular+cfs.patch. (the effects of the original bug are 
> > mostly harmless, the rbtree position gets corrected the first time the 
> > parent reschedules. The fix might improve heavy forker handling.)
> 
> It looks like it did not reach your public dir yet.
> 
> BTW, I've given it a try. It seems pretty usable. I have also tried
> the usual meaningless "glxgears" test with 12 of them at the same time,
> and they rotate very smoothly, there is absolutely no pause in any of
> them. But they don't all run at same speed, and top reports their CPU
> load varying from 3.4 to 10.8%, with what looks like more CPU is
> assigned to the first processes, and less CPU for the last ones. But
> this is just a rough observation on a stupid test, I would not call
> that one scientific in any way (and X has its share in the test too).

Follow-up: I think this is mostly X-related. I've started 100 scheddos,
and all get the same CPU percentage. Interestingly, mpg123 in parallel
does never skip at all because it needs quite less than 1% CPU and gets
its fair share at a load of 112. Xterms are slow to respond to typing
with the 12 gears and 100 scheddos, and expectedly it was X which was
starving. renicing it to -5 restores normal feeling with very slow
but smooth gear rotations. Leaving X niced at 0 and killing the gears
also restores normal behaviour.

All in all, it seems logical that processes which serve many others
become a bottleneck for them.

Forking becomes very slow above a load of 100 it seems. Sometimes,
the shell takes 2 or 3 seconds to return to prompt after I run
"scheddos &"

Those are very promising results, I nearly observe the same responsiveness
as I had on a solaris 10 with 10k running processes on a bigger machine.

I would be curious what a mysql test result would look like now.

Regards,
Willy

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