Re: specjbb2005 and aim7 regression with 2.6.32-rc kernels

From: Ingo Molnar
Date: Fri Nov 06 2009 - 03:04:35 EST

* Zhang, Yanmin <yanmin_zhang@xxxxxxxxxxxxxxx> wrote:

> Comparing with 2.6.31, specjbb2005 and aim7 have some regressions with
> 2.6.32-rc kernels on core2 machines.
> 1) On 4*4 core tigerton: specjbb2005 has about 5% regression.
> 2) On 2*4 stoakley: aim7 has about 5% regression.
> On Nehalem, specjbb2005 has about 2%~8% improvement instead of
> regression.
> aim7 has much dependency on schedule patameters, such like
> sched_latency_ns, sched_min_granularity_ns, and
> sched_wakeup_granularity_ns. 2.6.32-rc kernel decreases these
> parameter values. I restore them and retest aim7 on stoakley. aim7
> regression becomes about 2% and specjbb2005 regression also becomes
> 2%. But on Nehalem, the improvement shrinks.

Which precise 2.6.32-rc commit have you tested?

Since v2.6.32-rc6 Linus's tree has this one too:

f685cea: sched: Strengthen buddies and mitigate buddy induced latencies

Which should improve things a bit. For 2.6.33 we have queued up these
two in -tip:

a1f84a3: sched: Check for an idle shared cache in select_task_rq_fair()
1b9508f: sched: Rate-limit newidle

If any of them fixes a performance regression we could still merge them
into 2.6.32 as well.

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