linux-kernel - Re: [git] CFS-devel, group scheduler, fixes

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Message-Id: <1190188261.9185.21.camel@Homer.simpson.net>
Date:	Wed, 19 Sep 2007 09:51:01 +0200
From:	Mike Galbraith <efault@....de>
To:	Tong Li <tong.n.li@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, dimm <dmitry.adamushko@...il.com>,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [git] CFS-devel, group scheduler, fixes

On Wed, 2007-09-19 at 08:28 +0200, Mike Galbraith wrote:
> Greetings,
> 
> On Tue, 2007-09-18 at 23:03 -0700, Tong Li wrote:
> > This patch attempts to improve CFS's SMP global fairness based on the new 
> > virtual time design.
> > 
> > Removed vruntime adjustment in set_task_cpu() as it skews global fairness.
> 
> Since I'm (still) encountering Xorg latency issues (which go away if
> load is hefty instead of light) even with that migration adjustment and
> synchronization, and am having difficulty nailing it down to a specific
> event, I'll test this immediately.

(had to apply manually to freshly pulled tree)

Drat.  This didn't cure the latency hits with a Xorg at nice -5 running
with a make -j2 at nice 0, but seems to have reinstated a latency issue
which was previously cured.

Xorg 1 sec. max latency samples:
(trimmed to only show >20ms latencies)
se.wait_max              :            23343582
se.wait_max              :            20119460
se.wait_max              :            20771573
se.wait_max              :            21084567
se.wait_max              :            31338500
se.wait_max              :            35368148
se.wait_max              :            39199642
se.wait_max              :            22889062
se.wait_max              :            40285501
se.wait_max              :            21002720
se.wait_max              :            21002266
se.wait_max              :            21680578
se.wait_max              :            22012913
se.wait_max              :            94646331
se.wait_max              :            29003693
se.wait_max              :            20812613

(boot with maxcpus=1 or nail X+make to one cpu and these latencies are
gone, so it does seem to be the migration logic - why i was so
interested in testing your patch)

The scenario which was previously cured was this:
taskset -c 1 nice -n 0 ./massive_intr 2 9999
taskset -c 1 nice -n 5 ./massive_intr 2 9999
click link
(http://pages.cs.wisc.edu/~shubu/talks/cachescrub-prdc2004.ppt) to bring
up browser and OpenOffice Impress.

Xorg (at nice -5 + above scenario) latency samples:
se.wait_max              :            57985337
se.wait_max              :            25163510
se.wait_max              :            37005538
se.wait_max              :            66986511
se.wait_max              :            53990868
se.wait_max              :            80976761
se.wait_max              :            96967501
se.wait_max              :            80989254
se.wait_max              :            53990897
se.wait_max              :           181963905
se.wait_max              :            85985181

	-Mike

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