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From: Mel Gorman <mgorman@techsingularity.net>
To: Jirka Hladky <jhladky@redhat.com>
Cc: Phil Auld <pauld@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	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: Thu, 7 May 2020 16:54:22 +0100	[thread overview]
Message-ID: <20200507155422.GD3758@techsingularity.net> (raw)
In-Reply-To: <CAE4VaGCf0P2ht+7nbGFHV8Dd=e4oDEUPNdRUUBokRWgKRxofAA@mail.gmail.com>

On Thu, May 07, 2020 at 05:24:17PM +0200, Jirka Hladky wrote:
> Hi Mel,
> 
> > > Yes, it's indeed OMP.  With low threads count, I mean up to 2x number of
> > > NUMA nodes (8 threads on 4 NUMA node servers, 16 threads on 8 NUMA node
> > > servers).
> >
> > Ok, so we know it's within the imbalance threshold where a NUMA node can
> > be left idle.
> 
> we have discussed today with my colleagues the performance drop for
> some workloads for low threads counts (roughly up to 2x number of NUMA
> nodes). We are worried that it can be a severe issue for some use
> cases, which require a full memory bandwidth even when only part of
> CPUs is used.
> 
> We understand that scheduler cannot distinguish this type of workload
> from others automatically. However, there was an idea for a * new
> kernel tunable to control the imbalance threshold *. Based on the
> purpose of the server, users could set this tunable. See the tuned
> project, which allows creating performance profiles [1].
> 

I'm not completely opposed to it but given that the setting is global,
I imagine it could have other consequences if two applications ran
at different times have different requirements. Given that it's OMP,
I would have imagined that an application that really cared about this
would specify what was needed using OMP_PLACES. Why would someone prefer
kernel tuning or a tuned profile over OMP_PLACES? After all, it requires
specific knowledge of the application even to know that a particular
tuned profile is needed.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2020-05-07 15:54 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 [this message]
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
2020-05-15 14:43                                       ` Jirka Hladky

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