ULE on ARM

[Warner Losh]

On Mar 7, 2014, at 7:25 AM, Ian Lepore <ian at FreeBSD.org> wrote:

> On Fri, 2014-03-07 at 18:14 +0400, Ruslan Bukin wrote:
>> I discovered just a couple of ARM kernel configs
>> uses SCHED_ULE, but all other uses SCHED_4BSD
>> 
>> any disadvantages to use ULE scheduler on ARM?
>> or it is just because of historical reasons?
>> 
>> I enabled ULE on Freescale Vybrid and running
>> it for a long time just fine.
>> 
>> according to my subjective impressions ULE
>> works better on ARM in sound applications
>> 
>> -Ruslan
> 
> The widespread advice from a few years ago was that ULE was better for
> SMP and 4BSD was better for UP.  I don't know whether that's still true
> (or whether it was ever true).  I do know that there are fewer responses
> on mailing lists of "try switching the scheduler to 4BSD" as a way of
> fixing problems these days.  I switched imx6 to ULE when adding SMP
> support for it.

It all depends on the workload. 4BSD is better for some SMP workloads,
while ULE is better for others. But as a general rule, Ian is right: 4BSD
tends to be better at UP interactive workloads, while ULE tends to be better
at MP work loads that have a larger compute element to them (complex
transactions).

Warner