On Wed, Apr 05, 2017 at 09:39:43AM +0200, Ingo Molnar wrote: > > While converting the existing users I tried to stick with the rules > > above however… well mostly CPUFREQ tries to temporary switch the CPU > > mask to do something on a certain CPU and then switches the mask back it > > its original value. So in theory `cpus_ptr' could or should be used. > > However if this is invoked in a migration disabled region (which is not > > the case because it would require something like preempt_disable() and > > set_cpus_allowed_ptr() might sleep so it can't be) then the "restore" > > part would restore the wrong mask. So it only looks strange and I go for > > the pointer… > > So maybe we could add the following facility: > > ptr = sched_migrate_to_cpu_save(cpu); > > ... > > sched_migrate_to_cpu_restore(ptr); > > ... and use it in the cpufreq code. Then -rt could simply define > migrate_disable() > to be:
Argh, no.... We have plenty of proper per-cpu kthreads / workqueue and other APIs to do this. Not to mention that implementing the above in a non-broken way has user visible side-effects, which ugly.
