On Wed, May 09, 2018 at 12:46:18PM +0200, Peter Zijlstra wrote: > On Mon, May 07, 2018 at 05:01:34PM -0400, Johannes Weiner wrote: > > > @@ -2038,6 +2038,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > > cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags); > > if (task_cpu(p) != cpu) { > > wake_flags |= WF_MIGRATED; > > + psi_ttwu_dequeue(p); > > set_task_cpu(p, cpu); > > } > > > > > +static inline void psi_ttwu_dequeue(struct task_struct *p) > > +{ > > + /* > > + * Is the task being migrated during a wakeup? Make sure to > > + * deregister its sleep-persistent psi states from the old > > + * queue, and let psi_enqueue() know it has to requeue. > > + */ > > + if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) { > > + struct rq_flags rf; > > + struct rq *rq; > > + int clear = 0; > > + > > + if (p->in_iowait) > > + clear |= TSK_IOWAIT; > > + if (p->flags & PF_MEMSTALL) > > + clear |= TSK_MEMSTALL; > > + > > + rq = __task_rq_lock(p, &rf); > > + update_rq_clock(rq); > > + psi_task_change(p, rq_clock(rq), clear, 0); > > + p->sched_psi_wake_requeue = 1; > > + __task_rq_unlock(rq, &rf); > > + } > > +} > > Yeah, no... not happening. > > We spend a lot of time to never touch the old rq->lock on wakeups. Mason > was the one pushing for that, so he should very well know this. > > The one cross-cpu atomic (iowait) is already a problem (the whole iowait > accounting being useless makes it even worse), adding significant remote > prodding is just really bad. Also, since all you need is the global number, I don't think you actually need any of this. See what we do for nr_uninterruptible. In general I think you want to (re)read loadavg.c some more, and maybe reuse a bit more of that. -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html