Re: aim7 -30% regression in 2.6.24-rc1

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

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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