linux-kernel - Re: BFS vs. mainline scheduler benchmarks and measurements

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Date:	Wed, 09 Sep 2009 11:17:49 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Nikos Chantziaras <realnc@...or.de>
Cc:	Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...e.hu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Con Kolivas <kernel@...ivas.org>, linux-kernel@...r.kernel.org
Subject: Re: BFS vs. mainline scheduler benchmarks and measurements

On Wed, 2009-09-09 at 12:05 +0300, Nikos Chantziaras wrote:

> Thank you for mentioning min_granularity.  After:
> 
>    echo 10000000 > /proc/sys/kernel/sched_latency_ns
>    echo 2000000 > /proc/sys/kernel/sched_min_granularity_ns

You might also want to do:

     echo 2000000 > /proc/sys/kernel/sched_wakeup_granularity_ns

That affects when a newly woken task will preempt an already running
task.

> I can clearly see an improvement: animations that are supposed to be 
> fluid "skip" much less now, and in one occasion (simply moving the video 
> window around) have been eliminated completely.  However, there seems to 
> be a side effect from having CONFIG_SCHED_DEBUG enabled; things seem to 
> be generally a tad more "jerky" with that option enabled, even when not 
> even touching the latency and granularity defaults.

There's more code in the scheduler with that enabled but unless you've
got a terrible high ctx rate that really shouldn't affect things.

Anyway, you can always poke at these numbers in the code, and like Mike
did, kill sched_init_granularity().



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