On 29/11/18 11:02, Daniel Lezcano wrote: > On 29/11/2018 10:58, Juri Lelli wrote: > > On 29/11/18 10:18, Daniel Lezcano wrote: > >> On 29/11/2018 08:04, Juri Lelli wrote: > >> > >> [ ... ] > >> > >>>> With or without this patch, it is the case: > >>>> > >>>> task1 task2 > >>>> | | > >>>> read("/sys/.../cpu1/cpu_capacity) | > >>>> | write("/sys/.../cpu1/cpu_capacity") > >>>> read("/sys/.../cpu2/cpu_capacity) | > >>>> > >>>> > >>>> There is no guarantee userspace can have a consistent view of the > >>>> capacity. As soon as it reads a capacity, it can be changed in its back. > >>> > >>> True, but w/o the mutex task1 could read different cpu_capacity values > >>> for a cluster (it actually can also with current implementation, we > >>> should grab the mutex in the read path as well if we want to avoid > >>> this). > >> > >> Even if the mutex is on the read path, the userspace can see different > >> capacities because it will read the cpu_capacity per cpu directory. > >> > >> The mutex will be take when reading cpu0/cpu_capacity, not for > >> cpu[0-9]/cpu_capacity. Between two reads, a write can happen because the > >> lock is released in between. > >> > >> Do you agree with the patch ? Or do you want me to drop it ? > > > > I don't actually have cases at hand that are showing regression with it, > > I was just trying to understand if we might potentially hit problems in > > the future. So, I'm not against this patch. :-) > > not-not-acked-by ? :)
:-) I'm not maintaining this, so, Reviewed-by: Juri Lelli <juri.le...@redhat.com>