Re: BFS vs. mainline scheduler benchmarks and measurements

[Nikos Chantziaras <realnc@arcor.de>]

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.