Message-ID: <4AA768B1.708@arcor.de>
Date: Wed, 09 Sep 2009 11:34:57 +0300
From: Nikos Chantziaras <realnc@arcor.de>
Organization: Lucas Barks
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To: Ingo Molnar <mingo@elte.hu>
CC: Jens Axboe <jens.axboe@oracle.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Con Kolivas <kernel@kolivas.org>, linux-kernel@vger.kernel.org,
       Mike Galbraith <efault@gmx.de>
Subject: Re: BFS vs. mainline scheduler benchmarks and measurements
References: <20090906205952.GA6516@elte.hu> <20090907094953.GP18599@kernel.dk> <20090907115750.GW18599@kernel.dk> <20090907141458.GD24507@elte.hu> <20090907173846.GB18599@kernel.dk> <20090907204458.GJ18599@kernel.dk> <20090908091304.GQ18599@kernel.dk> <1252423398.7746.97.camel@twins> <20090908203409.GJ18599@kernel.dk> <20090909061308.GA28109@elte.hu>
In-Reply-To: <20090909061308.GA28109@elte.hu>
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On 09/09/2009 09:13 AM, Ingo Molnar wrote:
>
> * Jens Axboe<jens.axboe@oracle.com>  wrote:
>
>> On Tue, Sep 08 2009, Peter Zijlstra wrote:
>>> On Tue, 2009-09-08 at 11:13 +0200, Jens Axboe wrote:
>>>> And here's a newer version.
>>>
>>> I tinkered a bit with your proglet and finally found the
>>> problem.
>>>
>>> You used a single pipe per child, this means the loop in
>>> run_child() would consume what it just wrote out until it got
>>> force preempted by the parent which would also get woken.
>>>
>>> This results in the child spinning a while (its full quota) and
>>> only reporting the last timestamp to the parent.
>>
>> Oh doh, that's not well thought out. Well it was a quick hack :-)
>> Thanks for the fixup, now it's at least usable to some degree.
>
> What kind of latencies does it report on your box?
>
> Our vanilla scheduler default latency targets are:
>
>    single-core: 20 msecs
>      dual-core: 40 msecs
>      quad-core: 60 msecs
>      opto-core: 80 msecs
>
> You can enable CONFIG_SCHED_DEBUG=y and set it directly as well via
> /proc/sys/kernel/sched_latency_ns:
>
>     echo 10000000>  /proc/sys/kernel/sched_latency_ns

I've tried values ranging from 10000000 down to 100000.  This results in 
the stalls/freezes being a bit shorter, but clearly still there.  It 
does not eliminate them.

If there's anything else I can try/test, I would be happy to do so.
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