linux-kernel - Re: aim7 -30% regression in 2.6.24-rc1

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Date:	Tue, 30 Oct 2007 08:26:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: aim7 -30% regression in 2.6.24-rc1

* Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:

> sub-bisecting captured patch 
> 38ad464d410dadceda1563f36bdb0be7fe4c8938(sched: uniform tunings) 
> caused 20% regression of aim7.
> 
> The last 10% should be also related to sched parameters, such like 
> sysctl_sched_min_granularity.

ah, interesting. Since you have CONFIG_SCHED_DEBUG enabled, could you 
please try to figure out what the best value for 
/proc/sys/kernel_sched_latency, /proc/sys/kernel_sched_nr_latency and 
/proc/sys/kernel_sched_min_granularity is?

there's a tuning constraint for kernel_sched_nr_latency: 

- kernel_sched_nr_latency should always be set to 
  kernel_sched_latency/kernel_sched_min_granularity. (it's not a free 
  tunable)

i suspect a good approach would be to double the value of 
kernel_sched_latency and kernel_sched_nr_latency in each tuning 
iteration, while keeping kernel_sched_min_granularity unchanged. That 
will excercise the tuning values of the 2.6.23 kernel as well.

	Ingo
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