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SubjectRe: busted CFS group load balancer?
Ken Chen wrote:
> On Mon, Nov 17, 2008 at 7:37 AM, Chris Friesen wrote:
>>> It appears that the fair-group load balancer in 2.6.27 does not work
>>> properly.
>> There was an issue fixed post 2.6.27 where the load balancer didn't work
>> properly if there was one task per group per cpu. You might try
>> backporting commit 38736f4 and see if that helps.
>
> Tested git commit 38736f4, it doesn't fix the problem I'm seeing.
>

I plugged in the same weights into my test app (groups 1 and 2 instead
of ant/bee) and got the results below for a 10-sec run. The "actual"
numbers give the overall average and then the values for each hog
separately. In this case we see that both tasks in group 2 ended up
sharing a cpu with one of the tasks from group 1.

group actual(%) expected(%) ctx switches max_latency(ms)
1 99.69(99.38/99.99) 99.81 160/262 4/0
2 0.31( 0.31/0.31) 0.19 32/33 391/375

I've only got a 2-way system. If the results really are that much worse
on larger systems, then that's going to cause problems for us as well.
I'll see if I can get some time on a bigger machine.

Chris


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