Re: 2.6.27-rc5 OLTP performance regression

[Peter Zijlstra]

On Mon, 2008-09-08 at 10:58 -0700, Ma, Chinang wrote:
> We found the group scheduler in 2.6.27-rc5 has negative performance
> impact on TPC Online Transaction Processing workload. The test was
> conducted on a dual-socket quad-core Xeon server. OLTP workload is
> disk i/o intensive and we have over 200 database shadow processes
> running in the server during this test.  Enabling group scheduler
> (CONFIG_GROUP_SCHED=y) reduced performance by 2.0%. Oprofile data
> indicates significant amount of cycles are spent in tg_shares_up().
>  This is new regression as we did not find the same issue with 2.6.26
> kernel group scheduler. Is anybody looking into group scheduler
> performance and any idea for reducing the performance impact? 

Because the .26 group scheduler wasn't SMP aware. The extra cost comes
from the fact that .27 is.

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