On 31 March 2016 at 14:34, Peter Zijlstra <[email protected]> wrote: > On Thu, Mar 31, 2016 at 02:14:50PM +0200, Vincent Guittot wrote: >> In fact, I looks for the sequence where the utilization of a rq is not >> updated until the next tick but i can't find it. > > No, util it always updated, however.. > >> If cpu doesn't share cache, task is added to wake list and an ipi is >> sent and the utilization. > > Here we run: > > ttwu_do_activate() > ttwu_activate() > activate_task() > enqueue_task() > p->sched_class->enqueue_task() := enqueue_task_fair() > update_load_avg() > update_cfs_rq_load_avg() > cfs_rq_util_change() > > On the local cpu, and we can indeed call out to have the frequency > changed. > >> Otherwise, we directly enqueue the task on >> the rq and the utilization is updated > > But here we run it on a remote cpu, so we cannot call out and the > frequency remains the same. > > So if a remote wakeup on the same LLC domain happens, utilization will > increase but we will not observe until the next tick.
ok. I forgot that we have the condition cpu == smp_processor_id() in cfs_rq_util_change.
