SCHED_ULE should not be the default

Steve Kargl sgk at
Mon Dec 12 15:52:00 UTC 2011

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 environments),
> and other give contra not being the case.
> 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.

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.

PS: search the list archives for "kargl and ULE".


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