On 03/17/20 14:35, Josh Don wrote: > On Wed, Mar 11, 2020 at 7:05 AM Qais Yousef <qais.yousef@xxxxxxx> wrote: > > > > This actually helps me fix a similar problem I faced in RT [1]. If multiple RT > > tasks wakeup at the same time we get a 'thundering herd' issue where they all > > end up going to the same CPU, just to be pushed out again. > > > > Beside this will help fix another problem for RT tasks fitness, which is > > a manifestation of the problem above. If two tasks wake up at the same time and > > they happen to run on a little cpu (but request to run on a big one), one of > > them will end up being migrated because find_lowest_rq() will return the first > > cpu in the mask for both tasks. > > > > I tested the API (not the change in sched/core.c) and it looks good to me. > > Nice, glad that the API already has another use case. Thanks for taking a look. > > > nit: cpumask_first_and() is better here? > > Yea, I would also prefer to use it, but the definition of > cpumask_first_and() follows this section, as it itself uses > cpumask_next_and(). > > > It might be a good idea to split the API from the user too. > > Not sure what you mean by this, could you clarify? I meant it'd be a good idea to split the cpumask API into its own patch and have a separate patch for the user in sched/core.c. But that was a small nit. If the user (in sched/core.c) somehow introduces a regression, reverting it separately should be trivial. Thanks -- Qais Yousef > > On Tue, Mar 17, 2020 at 12:24 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > Anyway, for the API. > > > > > > Reviewed-by: Qais Yousef <qais.yousef@xxxxxxx> > > > Tested-by: Qais Yousef <qais.yousef@xxxxxxx> > > > > Thanks guys! > > Thanks Peter, any other comments or are you happy with merging this patch as-is?
