From: Johannes Weiner <hannes@cmpxchg.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tejun Heo <tj@kernel.org>, Suren Baghdasaryan <surenb@google.com>,
Daniel Drake <drake@endlessm.com>,
Vinayak Menon <vinmenon@codeaurora.org>,
Christopher Lameter <cl@linux.com>,
Mike Galbraith <efault@gmx.de>,
Shakeel Butt <shakeelb@google.com>,
Peter Enderborg <peter.enderborg@sony.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO
Date: Mon, 6 Aug 2018 11:40:51 -0400 [thread overview]
Message-ID: <20180806154051.GA14209@cmpxchg.org> (raw)
In-Reply-To: <20180806152528.GM2494@hirez.programming.kicks-ass.net>
On Mon, Aug 06, 2018 at 05:25:28PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 06, 2018 at 11:05:50AM -0400, Johannes Weiner wrote:
> > Argh, that's right. This needs an explicit count if we want to access
> > it locklessly. And you already said you didn't like that this is the
> > only state not derived purely from the task counters, so maybe this is
> > the way to go after all.
> >
> > How about something like this (untested)?
>
>
> > +static inline void psi_switch(struct rq *rq, struct task_struct *prev,
> > + struct task_struct *next)
> > +{
> > + if (psi_disabled)
> > + return;
> > +
> > + if (unlikely(prev->flags & PF_MEMSTALL))
> > + psi_task_change(prev, rq_clock(rq), TSK_RECLAIMING, 0);
> > + if (unlikely(next->flags & PF_MEMSTALL))
> > + psi_task_change(next, rq_clock(rq), 0, TSK_RECLAIMING);
> > +}
>
>
> Urgh... can't say I really like that.
>
> I would really rather do that scheduler_tick() thing to avoid the remote
> update. The tick is a lot less hot than the switch path and esp.
> next->flags might be a cold line (prev->flags is typically the same line
> as prev->state so we already have that, but I don't think anybody now
> looks at next->flags or its line, so that'd be cold load).
Okay, the tick updater sounds like a much better option then. HZ
frequency should produce more than recent enough data.
That means we will retain the not-so-nice PF_MEMSTALL flag test under
rq lock, but it'll eliminate most of that memory ordering headache.
I'll do that. Thanks!
next prev parent reply other threads:[~2018-08-06 15:37 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-01 15:19 [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v3 Johannes Weiner
2018-08-01 15:19 ` [PATCH 1/9] mm: workingset: don't drop refault information prematurely Johannes Weiner
2018-08-01 15:19 ` [PATCH 2/9] mm: workingset: tell cache transitions from workingset thrashing Johannes Weiner
2018-08-01 21:56 ` Suren Baghdasaryan
2018-08-02 12:28 ` Johannes Weiner
2018-08-01 15:19 ` [PATCH 3/9] delayacct: track delays from thrashing cache pages Johannes Weiner
2018-08-01 15:19 ` [PATCH 4/9] sched: loadavg: consolidate LOAD_INT, LOAD_FRAC, CALC_LOAD Johannes Weiner
2018-08-01 15:19 ` [PATCH 5/9] sched: loadavg: make calc_load_n() public Johannes Weiner
2018-08-01 15:19 ` [PATCH 6/9] sched: sched.h: make rq locking and clock functions available in stats.h Johannes Weiner
2018-08-01 15:19 ` [PATCH 7/9] sched: introduce this_rq_lock_irq() Johannes Weiner
2018-08-01 15:19 ` [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
2018-08-03 16:56 ` Peter Zijlstra
2018-08-06 15:05 ` Johannes Weiner
2018-08-06 15:25 ` Peter Zijlstra
2018-08-06 15:40 ` Johannes Weiner [this message]
2018-08-06 15:19 ` Johannes Weiner
2018-08-06 16:03 ` Peter Zijlstra
2018-08-21 19:44 ` Johannes Weiner
2018-08-22 9:16 ` Peter Zijlstra
2018-08-03 17:07 ` Peter Zijlstra
2018-08-06 15:23 ` Johannes Weiner
2018-08-03 17:15 ` Peter Zijlstra
2018-08-03 17:21 ` Peter Zijlstra
2018-08-21 20:11 ` Johannes Weiner
2018-08-22 9:10 ` Peter Zijlstra
2018-08-22 17:28 ` Johannes Weiner
2018-08-01 15:19 ` [PATCH 9/9] psi: cgroup support Johannes Weiner
2018-08-07 11:50 ` [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v3 peter enderborg
2018-08-07 17:51 ` Johannes Weiner
-- strict thread matches above, loose matches on Subject: below --
2018-08-28 17:22 [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v4 Johannes Weiner
2018-08-28 17:22 ` [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
2018-08-28 20:11 ` Randy Dunlap
2018-08-28 20:56 ` Johannes Weiner
2018-08-28 21:30 ` Randy Dunlap
2018-09-07 10:16 ` Peter Zijlstra
2018-09-07 10:21 ` Peter Zijlstra
2018-09-07 14:44 ` Johannes Weiner
2018-09-07 14:58 ` Peter Zijlstra
2018-09-07 17:50 ` Johannes Weiner
2018-09-07 10:24 ` Peter Zijlstra
2018-09-07 14:54 ` Johannes Weiner
2018-08-01 15:12 Johannes Weiner
2018-08-01 15:13 ` [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
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