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

On Wed, 19 Sep 2007, Mike Galbraith wrote:

On Wed, 2007-09-19 at 09:51 +0200, Mike Galbraith wrote:

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

To be doubly sure of the effect on the pinned tasks + migrating Xorg
scenario, I just ran the above test 10 times with virgin devel source.
Maximum Xorg latency was 20ms.

	-Mike

Yeah, the patch was a first attempt at getting better global fairness for unpinned tasks. I expected there'd be latency problems when unpinned and pinned tasks co-exist. The original code for vruntime adjustment in set_task_cpu() helped alleviate this problem, so removing it in my patch would definitely bring the problem back. On the other hand, leaving it there broke global fairness in my fairness benchmark. So we'd need a better compromise.

Were the experiments run on a 2-CPU system? When Xorg experiences large wait time, is it on the same CPU that has the two pinned tasks? If this is the case, then the problem could be X somehow advanced faster and got a larger vruntime then the two pinned tasks, so it had to wait for the pinned ones to catch up before it got a chance to be scheduled.

  tong
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