Re: [PATCH v3 09/22] sched: compute runnable load avg in cpu_loadand cpu_avg_load_per_task

[Alex Shi]

On 01/07/2013 02:31 AM, Linus Torvalds wrote:
> On Sat, Jan 5, 2013 at 11:54 PM, Alex Shi <alex.shi@xxxxxxxxx> wrote:
>>
>> I just looked into the aim9 benchmark, in this case it forks 2000 tasks,
>> after all tasks ready, aim9 give a signal than all tasks burst waking up
>> and run until all finished.
>> Since each of tasks are finished very quickly, a imbalanced empty cpu
>> may goes to sleep till a regular balancing give it some new tasks. That
>> causes the performance dropping. cause more idle entering.
> 
> Sounds like for AIM (and possibly for other really bursty loads), we
> might want to do some load-balancing at wakeup time by *just* looking
> at the number of running tasks, rather than at the load average. Hmm?
> 
> The load average is fundamentally always going to run behind a bit,
> and while you want to use it for long-term balancing, a short-term you
> might want to do just a "if we have a huge amount of runnable
> processes, do a load balancing *now*". Where "huge amount" should
> probably be relative to the long-term load balancing (ie comparing the
> number of runnable processes on this CPU right *now* with the load
> average over the last second or so would show a clear spike, and a
> reason for quick action).
> 

Sorry for response late!

Just written a patch following your suggestion, but no clear improvement for this case.
I also tried change the burst checking interval, also no clear help.

If I totally give up runnable load in periodic balancing, the performance can recover 60%
of lose.

I will try to optimize wake up balancing in weekend.

Nice weekend!
Alex

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