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

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Date:	Wed, 09 Sep 2009 23:12:14 +0300
From:	Nikos Chantziaras <realnc@...or.de>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jens Axboe <jens.axboe@...cle.com>, Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Con Kolivas <kernel@...ivas.org>, linux-kernel@...r.kernel.org
Subject: Re: BFS vs. mainline scheduler benchmarks and measurements

On 09/09/2009 09:04 PM, Ingo Molnar wrote:
> [...]
> * Jens Axboe<jens.axboe@...cle.com>  wrote:
>
>> On Wed, Sep 09 2009, Jens Axboe wrote:
>>  [...]
>> BFS210 runs on the laptop (dual core intel core duo). With make -j4
>> running, I clock the following latt -c8 'sleep 10' latencies:
>>
>> -rc9
>>
>>          Max                17895 usec
>>          Avg                 8028 usec
>>          Stdev               5948 usec
>>          Stdev mean           405 usec
>>
>>          Max                17896 usec
>>          Avg                 4951 usec
>>          Stdev               6278 usec
>>          Stdev mean           427 usec
>>
>>          Max                17885 usec
>>          Avg                 5526 usec
>>          Stdev               6819 usec
>>          Stdev mean           464 usec
>>
>> -rc9 + mike
>>
>>          Max                 6061 usec
>>          Avg                 3797 usec
>>          Stdev               1726 usec
>>          Stdev mean           117 usec
>>
>>          Max                 5122 usec
>>          Avg                 3958 usec
>>          Stdev               1697 usec
>>          Stdev mean           115 usec
>>
>>          Max                 6691 usec
>>          Avg                 2130 usec
>>          Stdev               2165 usec
>>          Stdev mean           147 usec
>
> At least in my tests these latencies were mainly due to a bug in
> latt.c - i've attached the fixed version.
>
> The other reason was wakeup batching. If you do this:
>
>     echo 0>  /proc/sys/kernel/sched_wakeup_granularity_ns
>
> ... then you can switch on insta-wakeups on -tip too.
>
> With a dual-core box and a make -j4 background job running, on
> latest -tip i get the following latencies:
>
>   $ ./latt -c8 sleep 30
>   Entries: 656 (clients=8)
>
>   Averages:
>   ------------------------------
>   	Max	      158 usec
> 	Avg	       12 usec
> 	Stdev	       10 usec

With your version of latt.c, I get these results with 2.6-tip vs 
2.6.31-rc9-bfs:


(mainline)
Averages:
------------------------------
         Max            50 usec
         Avg            12 usec
         Stdev           3 usec


(BFS)
Averages:
------------------------------
         Max           474 usec
         Avg            11 usec
         Stdev          16 usec


However, the interactivity problems still remain.  Does that mean it's 
not a latency issue?
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