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From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Jirka Hladky <jhladky@redhat.com>, Phil Auld <pauld@redhat.com>,
	Ingo Molnar <mingo@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Hillf Danton <hdanton@sina.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Douglas Shakshober <dshaks@redhat.com>,
	Waiman Long <longman@redhat.com>, Joe Mario <jmario@redhat.com>,
	Bill Gray <bgray@redhat.com>
Subject: Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6
Date: Fri, 15 May 2020 14:51:28 +0200	[thread overview]
Message-ID: <20200515125128.GU2957@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200515122231.GL3758@techsingularity.net>

On Fri, May 15, 2020 at 01:22:31PM +0100, Mel Gorman wrote:
> On Fri, May 15, 2020 at 01:28:15PM +0200, Peter Zijlstra wrote:

> > > +			if (val & _TIF_POLLING_NRFLAG)
> > > +				goto activate;
> > 
> > I'm completely confused... the result here is that if you're polling you
> > do _NOT_ queue on the wake_list, but instead immediately enqueue.
> > 
> > (which kinda makes sense, since if the remote CPU is idle, it doesn't
> > have these lines in its cache anyway)
> > 
> 
> Crap, I rushed this and severely confused myself about what is going

Hehe, and here I though I was confused :-)

> on. It is definitely the case that flipping this check does not give
> any benefit. The patch shows a benefit but I'm failing to understand
> exactly why. How I ended up here was perf indicating a lot of time spent
> on smp_cond_load_acquire() which made me look closely at ttwu_remote()
> and looking at function graphs to compare the different types of wakeups
> and their timings.

So the raisin we did this remote wakeup thing in the first place was
that Oracle was having very heavy rq->lock cache-line contention. By
farming off the enqueue to the CPU that was going to run the task
anyway, the rq->lock (and the other runqueue structure lines) could stay
in the CPU that was using them (hard). Less cacheline ping-pong, more
win.

The observation here is that if a CPU is idle, it's rq will not be
contended.

  reply	other threads:[~2020-05-15 12:52 UTC|newest]

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-24  9:52 [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6 Mel Gorman
2020-02-24  9:52 ` [PATCH 01/13] sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression Mel Gorman
2020-02-24  9:52 ` [PATCH 02/13] sched/numa: Trace when no candidate CPU was found on the preferred node Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2020-02-24  9:52 ` [PATCH 03/13] sched/numa: Distinguish between the different task_numa_migrate failure cases Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] sched/numa: Distinguish between the different task_numa_migrate() " tip-bot2 for Mel Gorman
2020-02-24  9:52 ` [PATCH 04/13] sched/fair: Reorder enqueue/dequeue_task_fair path Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2020-02-24  9:52 ` [PATCH 05/13] sched/numa: Replace runnable_load_avg by load_avg Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2020-02-24  9:52 ` [PATCH 06/13] sched/numa: Use similar logic to the load balancer for moving between domains with spare capacity Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2020-02-24  9:52 ` [PATCH 07/13] sched/pelt: Remove unused runnable load average Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2020-02-24  9:52 ` [PATCH 08/13] sched/pelt: Add a new runnable average signal Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2020-02-24 16:01     ` Valentin Schneider
2020-02-24 16:34       ` Mel Gorman
2020-02-25  8:23       ` Vincent Guittot
2020-02-24  9:52 ` [PATCH 09/13] sched/fair: Take into account runnable_avg to classify group Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Vincent Guittot
2020-02-24  9:52 ` [PATCH 10/13] sched/numa: Prefer using an idle cpu as a migration target instead of comparing tasks Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] sched/numa: Prefer using an idle CPU " tip-bot2 for Mel Gorman
2020-02-24  9:52 ` [PATCH 11/13] sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2020-02-24  9:52 ` [PATCH 12/13] sched/numa: Bias swapping tasks based on their preferred node Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2020-02-24  9:52 ` [PATCH 13/13] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found Mel Gorman
2020-02-24 15:20   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2020-02-24 15:16 ` [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6 Ingo Molnar
2020-02-25 11:59   ` Mel Gorman
2020-02-25 13:28     ` Vincent Guittot
2020-02-25 14:24       ` Mel Gorman
2020-02-25 14:53         ` Vincent Guittot
2020-02-27  9:09         ` Ingo Molnar
2020-03-09 19:12 ` Phil Auld
2020-03-09 20:36   ` Mel Gorman
2020-03-12  9:54     ` Mel Gorman
2020-03-12 12:17       ` Jirka Hladky
     [not found]       ` <CAE4VaGA4q4_qfC5qe3zaLRfiJhvMaSb2WADgOcQeTwmPvNat+A@mail.gmail.com>
2020-03-12 15:56         ` Mel Gorman
2020-03-12 17:06           ` Jirka Hladky
     [not found]           ` <CAE4VaGD8DUEi6JnKd8vrqUL_8HZXnNyHMoK2D+1-F5wo+5Z53Q@mail.gmail.com>
2020-03-12 21:47             ` Mel Gorman
2020-03-12 22:24               ` Jirka Hladky
2020-03-20 15:08                 ` Jirka Hladky
     [not found]                 ` <CAE4VaGC09OfU2zXeq2yp_N0zXMbTku5ETz0KEocGi-RSiKXv-w@mail.gmail.com>
2020-03-20 15:22                   ` Mel Gorman
2020-03-20 15:33                     ` Jirka Hladky
     [not found]                     ` <CAE4VaGBGbTT8dqNyLWAwuiqL8E+3p1_SqP6XTTV71wNZMjc9Zg@mail.gmail.com>
2020-03-20 16:38                       ` Mel Gorman
2020-03-20 17:21                         ` Jirka Hladky
2020-05-07 15:24                         ` Jirka Hladky
2020-05-07 15:54                           ` Mel Gorman
2020-05-07 16:29                             ` Jirka Hladky
2020-05-07 17:49                               ` Phil Auld
     [not found]                                 ` <20200508034741.13036-1-hdanton@sina.com>
2020-05-18 14:52                                   ` Jirka Hladky
     [not found]                                     ` <20200519043154.10876-1-hdanton@sina.com>
2020-05-20 13:58                                       ` Jirka Hladky
2020-05-20 16:01                                         ` Jirka Hladky
2020-05-21 11:06                                         ` Mel Gorman
     [not found]                                         ` <20200521140931.15232-1-hdanton@sina.com>
2020-05-21 16:04                                           ` Mel Gorman
     [not found]                                           ` <20200522010950.3336-1-hdanton@sina.com>
2020-05-22 11:05                                             ` Mel Gorman
2020-05-08  9:22                               ` Mel Gorman
2020-05-08 11:05                                 ` Jirka Hladky
     [not found]                                 ` <CAE4VaGC_v6On-YvqdTwAWu3Mq4ofiV0pLov-QpV+QHr_SJr+Rw@mail.gmail.com>
2020-05-13 14:57                                   ` Jirka Hladky
2020-05-13 15:30                                     ` Mel Gorman
2020-05-13 16:20                                       ` Jirka Hladky
2020-05-14  9:50                                         ` Mel Gorman
     [not found]                                           ` <CAE4VaGCGUFOAZ+YHDnmeJ95o4W0j04Yb7EWnf8a43caUQs_WuQ@mail.gmail.com>
2020-05-14 10:08                                             ` Mel Gorman
2020-05-14 10:22                                               ` Jirka Hladky
2020-05-14 11:50                                                 ` Mel Gorman
2020-05-14 13:34                                                   ` Jirka Hladky
2020-05-14 15:31                                       ` Peter Zijlstra
2020-05-15  8:47                                         ` Mel Gorman
2020-05-15 11:17                                           ` Peter Zijlstra
2020-05-15 13:03                                             ` Mel Gorman
2020-05-15 13:12                                               ` Peter Zijlstra
2020-05-15 13:28                                                 ` Peter Zijlstra
2020-05-15 14:24                                             ` Peter Zijlstra
2020-05-21 10:38                                               ` Mel Gorman
2020-05-21 11:41                                                 ` Peter Zijlstra
2020-05-22 13:28                                                   ` Mel Gorman
2020-05-22 14:38                                                     ` Peter Zijlstra
2020-05-15 11:28                                           ` Peter Zijlstra
2020-05-15 12:22                                             ` Mel Gorman
2020-05-15 12:51                                               ` Peter Zijlstra [this message]
2020-05-15 14:43                                       ` Jirka Hladky

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