Subject: Re: aim7 -30% regression in 2.6.24-rc1
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: LKML <linux-kernel@vger.kernel.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
In-Reply-To: <20071030072658.GB20372@elte.hu>
References: <1193391787.3019.174.camel@ymzhang>
	 <20071026112307.GA30406@elte.hu> <1193624538.3019.189.camel@ymzhang>
	 <1193650626.3019.198.camel@ymzhang> <1193710325.3019.203.camel@ymzhang>
	 <20071030072658.GB20372@elte.hu>
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Date: Tue, 30 Oct 2007 16:36:30 +0800
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On Tue, 2007-10-30 at 08:26 +0100, Ingo Molnar wrote:
> * Zhang, Yanmin <yanmin_zhang@linux.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.
I followed your idea to test 2.6.24-rc1. The improvement is slow.
When sched_nr_latency=2560 and sched_latency_ns=640000000, the performance
is still about 15% less than 2.6.23.

-yanmin
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