SCHED_ULE should not be the default

[mdf at FreeBSD.org]

On Mon, Dec 12, 2011 at 7:32 AM, Gary Jennejohn
<gljennjohn at googlemail.com> wrote:
> On Mon, 12 Dec 2011 15:13:00 +0000
> Vincent Hoffman <vince at unsane.co.uk> wrote:
>
>>
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>> On 12/12/2011 13:47, O. Hartmann wrote:
>> >
>> >> Not fully right, boinc defaults to run on idprio 31 so this isn't an
>> >> issue. And yes, there are cases where SCHED_ULE shows much better
>> >> performance then SCHED_4BSD. [...]
>> >
>> > Do we have any proof at hand for such cases where SCHED_ULE performs
>> > much better than SCHED_4BSD? Whenever the subject comes up, it is
>> > mentioned, that SCHED_ULE has better performance on boxes with a ncpu >
>> > 2. But in the end I see here contradictionary statements. People
>> > complain about poor performance (especially in scientific environments),
>> > and other give contra not being the case.
>> It all a little old now but some if the stuff in
>> http://people.freebsd.org/~kris/scaling/
>> covers improvements that were seen.
>>
>> http://jeffr-tech.livejournal.com/5705.html
>> shows a little too, reading though Jeffs blog is worth it as it has some
>> interesting stuff on SHED_ULE.
>>
>> I thought there were some more benchmarks floating round but cant find
>> any with a quick google.
>>
>>
>> Vince
>>
>> >
>> > Within our department, we developed a highly scalable code for planetary
>> > science purposes on imagery. It utilizes present GPUs via OpenCL if
>> > present. Otherwise it grabs as many cores as it can.
>> > By the end of this year I'll get a new desktop box based on Intels new
>> > Sandy Bridge-E architecture with plenty of memory. If the colleague who
>> > developed the code is willing performing some benchmarks on the same
>> > hardware platform, we'll benchmark bot FreeBSD 9.0/10.0 and the most
>> > recent Suse. For FreeBSD I intent also to look for performance with both
>> > different schedulers available.
>> >
>
> These observations are not scientific, but I have a CPU from AMD with
> 6 cores (AMD Phenom(tm) II X6 1090T Processor).
>
> My simple test was ``make buildkernel'' while watching the core usage with
> gkrellm.
>
> With SCHED_4BSD all 6 cores are loaded to 97% during the build phase.
> I've never seen any value above 97% with gkrellm.
>
> With SCHED_ULE I never saw all 6 cores loaded this heavily.  Usually
> 2 or more cores were at or below 90%.  Not really that significant, but
> still a noticeable difference in apparent scheduling behavior.  Whether
> the observed difference is due to some change in data from the kernel to
> gkrellm is beyond me.

SCHED_ULE is much sloppier about calculating which thread used a
timeslice -- unless the timeslice went 100% to a thread, the fraction
it used may get attributed elsewhere.  So top's reporting of thread
usage is not a useful metric.  Total buildworld time is, potentially.

Thanks,
matthew