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

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Date:	Wed, 09 Sep 2009 13:17:59 +0300
From:	Nikos Chantziaras <realnc@...or.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 09/09/2009 12:40 PM, Nikos Chantziaras wrote:
> On 09/09/2009 12:17 PM, Peter Zijlstra wrote:
>> 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.
>
> Lowering wakeup_granularity seems to make things worse in an interesting
> way:
>
> With low wakeup_granularity, the video itself will start skipping if I
> move the window around. However, the window manager's effect of moving a
> window around is smooth.
>
> With high wakeup_granularity, the video itself will not skip while
> moving the window around. But this time, the window manager's effect of
> the window move is skippy.
>
> (I should point out that only with the BFS-patched kernel can I have a
> smooth video *and* a smooth window-moving effect at the same time.)
> Mainline seems to prioritize one of the two according to whether
> wakeup_granularity is raised or lowered. However, I have not tested
> Mike's patch yet (but will do so ASAP.)

I've tested Mike's patch and it achieves the same effect as raising 
sched_min_granularity.

To round it up:

By testing various values for sched_latency_ns, sched_min_granularity_ns 
and sched_wakeup_granularity_ns, I can achieve three results:

   1. Fluid animations for the foreground app, skippy ones for
      the rest (video plays nicely, rest of the desktop lags.)

   2. Fluid animations for the background apps, a skippy one for
      the one in the foreground (dekstop behaves nicely, video lags.)

   3. Equally skippy/jerky behavior for all of them.

Unfortunately, a "4. Equally fluid behavior for all of them" cannot be 
achieved with mainline, unless I missed some other tweak.
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