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SubjectRe: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO
On Fri, Jul 13, 2018 at 12:17:56PM -0400, Johannes Weiner wrote:
> On Fri, Jul 13, 2018 at 11:21:53AM +0200, Peter Zijlstra wrote:
> > On Thu, Jul 12, 2018 at 01:29:40PM -0400, Johannes Weiner wrote:
> > > +static inline void psi_ttwu_dequeue(struct task_struct *p)
> > > +{
> > > + if (psi_disabled)
> > > + return;
> > > + /*
> > > + * 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);
> > > + }
> > > +}
> >
> > Still NAK, what happened to this here:

> That's my thought process, anyway. I'd be more than happy to make this
> more lightweight, but I don't see a way to do it without losing
> significant functional precision.

I think you're going to have to. We put a lot of effort into not taking
the old rq->lock on remote wakeups and got a significant performance
benefit from that.

You just utterly destroyed that for workloads with a high number of
iowait wakeups.
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