Valentin Schneider <vschneid@xxxxxxxxxx> writes: > On 18/07/24 17:25, Benjamin Segall wrote: >> Valentin Schneider <vschneid@xxxxxxxxxx> writes: >> >>> I've tested a 10ms runtime / 100ms period cgroup with an always running >>> task: upstream gets a "clean" periodic pattern of 10ms runtime every 100ms, >>> whereas this gets something more like 40ms runtime every 400ms. >> >> Hmm, this seems a little odd since TWA_RESUME does a kick_process. > > I didn't ponder too much on the workload used here, but the point I wanted > to bring up is: if you give a cgroup X amount of runtime, it may still > consume more than that within a single period because execution in > kernelspace isn't immediately stopped/throttled. > > It means the "standard" bandwidth control behaviour becomes a bit more > bursty. Yeah, more bursty behavior when doing cpu-burning syscalls is expected. With the check on exit to user I wouldn't expect anything worse than the duration of the syscall though, so it depends on what your test was. >>> + >>> + /* >>> + * Account tasks woken up in children; by this point all direct children >>> + * have been visited. >>> + */ >>> + task_delta += cfs_rq->unthrottled_h_nr_running; >>> + idle_task_delta += cfs_rq->unthrottled_idle_h_nr_running; >>> + >>> + cfs_rq->h_nr_running += task_delta; >>> + cfs_rq->idle_h_nr_running += idle_task_delta; >>> + >>> + /* >>> + * unthrottle_cfs_rq() needs a value to up-propagate above the >>> + * freshly unthrottled cfs_rq. >>> + */ >>> + cfs_rq->unthrottled_h_nr_running = task_delta; >>> + cfs_rq->unthrottled_idle_h_nr_running = idle_task_delta; >> >> I think this should have no effect, right? > > Hm so my thoughts here are: > The walk_tg_tree_from(tg_unthrottle_up) will update *nr_running counts up > to the cfs_rq->tg->se[cpu_of(rq)]. However if that cfs_rq isn't the root > one, we'll need the for_each_sched_entity() loop further down > unthrottle_cfs_rq() to update the upper part of the hierarchy. The values > that will be up-propagated there are the ones being saved here. I'm pretty sure this comment was left over from when I didn't understand what they were being used for. I'm pretty sure I remember intending to remove it.
