SCHED_ULE should not be the default
malin.randstrom at gmail.com
Tue Dec 13 21:58:23 UTC 2011
stop sending me spam mail ... you never stop despite me having unsubscribeb
several times. stop this!
On Dec 13, 2011 8:12 PM, "Steve Kargl" <sgk at troutmask.apl.washington.edu>
> On Tue, Dec 13, 2011 at 02:23:46PM +0100, O. Hartmann wrote:
> > On 12/12/11 16:51, Steve Kargl wrote:
> > > On Mon, Dec 12, 2011 at 02:47:57PM +0100, 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
> > >> and other give contra not being the case.
> > >>
> > >> Within our department, we developed a highly scalable code for
> > >> 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
> > >> 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
> > >> different schedulers available.
> > >>
> > >
> > > This comes up every 9 months or so, and must be approaching
> > > FAQ status.
> > >
> > > In a HPC environment, I recommend 4BSD. Depending on
> > > the workload, ULE can cause a severe increase in turn
> > > around time when doing already long computations. If
> > > you have an MPI application, simply launching greater
> > > than ncpu+1 jobs can show the problem.
> > Well, those recommendations should based on "WHY". As the mostly
> > negative experiences with SCHED_ULE in highly computative workloads get
> > allways contradicted by "...but there are workloads that show the
> > opposite ..." this should be shown by more recent benchmarks and
> > explanations than legacy benchmarks from years ago.
> I have given the WHY in previous discussions of ULE, based
> on what you call legacy benchmarks. I have not seen any
> commit to sched_ule.c that would lead me to believe that
> the performance issues with ULE and cpu-bound numerical
> codes have been addressed. Repeating the benchmark would
> be a waste of time.
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