On Tue, May 22, 2018 at 2:22 PM, Rafael J. Wysocki <r...@rjwysocki.net> wrote: > On Tuesday, May 22, 2018 1:42:05 PM CEST Rafael J. Wysocki wrote: >> On Tue, May 22, 2018 at 1:38 PM, Viresh Kumar <viresh.ku...@linaro.org> >> wrote: >> > On 22-05-18, 13:31, Rafael J. Wysocki wrote: >> >> So below is my (compiled-only) version of the $subject patch, obviously >> >> based >> >> on the Joel's work. >> >> >> >> Roughly, what it does is to move the fast_switch_enabled path entirely to >> >> sugov_update_single() and take the spinlock around sugov_update_commit() >> >> in the one-CPU case too. > > [cut] > >> > >> > Why do you assume that fast switch isn't possible in shared policy >> > cases ? It infact is already enabled for few drivers. > > I hope that fast_switch is not used with devfs_possible_from_any_cpu set in > the > one-CPU policy case, as that looks racy even without any patching.
Which would be the only case in which sugov_update_single() would run on a CPU that is not the target. And running sugov_update_single() concurrently on two different CPUs for the same target is a no-no, as we don't prevent concurrent updates from occurring in that path. Which means that the original patch from Joel will be sufficient as long as we ensure that sugov_update_single() can only run on one CPU at a time.