Re: [PATCH v2] sched/core: Don't mix isolcpus and housekeeping CPUs

From: Peter Zijlstra
Date: Wed Oct 24 2018 - 06:15:24 EST

On Wed, Oct 24, 2018 at 03:16:46PM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> [2018-10-24 09:56:36]:
> > On Wed, Oct 24, 2018 at 08:32:49AM +0530, Srikar Dronamraju wrote:
> > It would certainly be a bit odd because the
> > application is asking for some protection but no guarantees are given
> > and the application is not made aware via an error code that there is a
> > problem. Asking the application to parse dmesg hoping to find the right
> > error message is going to be fragile.
> Its a actually a good question.
> What should we be doing if a mix of isolcpus and housekeeping (aka
> non-isolcpus) is given in the mask.
> Right now as you pointed, there is no easy way for the application to know
> which are the non-isolcpus to set its affinity. cpusets effective_cpus and
> cpus_allowed both will contain isolcpus too.

The easy option is to not use isolcpus :-) It is a horrifically bad