From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Phil Auld <pauld@redhat.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Quentin Perret <quentin.perret@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Hillf Danton <hdanton@sina.com>, Parth Shah <parth@linux.ibm.com>,
Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH v4 04/11] sched/fair: rework load_balance
Date: Fri, 8 Nov 2019 18:37:30 +0000 [thread overview]
Message-ID: <20191108183730.GU3016@techsingularity.net> (raw)
In-Reply-To: <20191108163501.GA26528@linaro.org>
On Fri, Nov 08, 2019 at 05:35:01PM +0100, Vincent Guittot wrote:
> > Fair enough, netperf hits the corner case where it does not work but
> > that is also true without your series.
>
> I run mmtest/netperf test on my setup. It's a mix of small positive or
> negative differences (see below)
>
> <SNIP>
>
> netperf-tcp
> 5.3-rc2 5.3-rc2
> tip +rwk+fix
> Hmean 64 871.30 ( 0.00%) 860.90 * -1.19%*
> Hmean 128 1689.39 ( 0.00%) 1679.31 * -0.60%*
> Hmean 256 3199.59 ( 0.00%) 3241.98 * 1.32%*
> Hmean 1024 9390.47 ( 0.00%) 9268.47 * -1.30%*
> Hmean 2048 13373.95 ( 0.00%) 13395.61 * 0.16%*
> Hmean 3312 16701.30 ( 0.00%) 17165.96 * 2.78%*
> Hmean 4096 15831.03 ( 0.00%) 15544.66 * -1.81%*
> Hmean 8192 19720.01 ( 0.00%) 20188.60 * 2.38%*
> Hmean 16384 23925.90 ( 0.00%) 23914.50 * -0.05%*
> Stddev 64 7.38 ( 0.00%) 4.23 ( 42.67%)
> Stddev 128 11.62 ( 0.00%) 10.13 ( 12.85%)
> Stddev 256 34.33 ( 0.00%) 7.94 ( 76.88%)
> Stddev 1024 35.61 ( 0.00%) 116.34 (-226.66%)
> Stddev 2048 285.30 ( 0.00%) 80.50 ( 71.78%)
> Stddev 3312 304.74 ( 0.00%) 449.08 ( -47.36%)
> Stddev 4096 668.11 ( 0.00%) 569.30 ( 14.79%)
> Stddev 8192 733.23 ( 0.00%) 944.38 ( -28.80%)
> Stddev 16384 553.03 ( 0.00%) 299.44 ( 45.86%)
>
> 5.3-rc2 5.3-rc2
> tip +rwk+fix
> Duration User 138.05 140.95
> Duration System 1210.60 1208.45
> Duration Elapsed 1352.86 1352.90
>
This roughly matches what I've seen. The interesting part to me for
netperf is the next section of the report that reports the locality of
numa hints. With netperf on a 2-socket machine, it's generally around
50% as the client/server are pulled apart. Because netperf is not
heavily memory bound, it doesn't have much impact on the overall
performance but it's good at catching the cross-node migrations.
> >
> > > I agree that additional patches are probably needed to improve load
> > > balance at NUMA level and I expect that this rework will make it
> > > simpler to add.
> > > I just wanted to get the output of some real use cases before defining
> > > more numa level specific conditions. Some want to spread on there numa
> > > nodes but other want to keep everything together. The preferred node
> > > and fbq_classify_group was the only sensible metrics to me when he
> > > wrote this patchset but changes can be added if they make sense.
> > >
> >
> > That's fair. While it was possible to address the case before your
> > series, it was a hatchet job. If the changelog simply notes that some
> > special casing may still be required for SD_NUMA but it's outside the
> > scope of the series, then I'd be happy. At least there is a good chance
> > then if there is follow-up work that it won't be interpreted as an
> > attempt to reintroduce hacky heuristics.
> >
>
> Would the additional comment make sense for you about work to be done
> for SD_NUMA ?
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0ad4b21..7e4cb65 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6960,11 +6960,34 @@ enum fbq_type { regular, remote, all };
> * group. see update_sd_pick_busiest().
> */
> enum group_type {
> + /*
> + * The group has spare capacity that can be used to process more work.
> + */
> group_has_spare = 0,
> + /*
> + * The group is fully used and the tasks don't compete for more CPU
> + * cycles. Nevetheless, some tasks might wait before running.
> + */
> group_fully_busy,
> + /*
> + * One task doesn't fit with CPU's capacity and must be migrated on a
> + * more powerful CPU.
> + */
> group_misfit_task,
> + /*
> + * One local CPU with higher capacity is available and task should be
> + * migrated on it instead on current CPU.
> + */
> group_asym_packing,
> + /*
> + * The tasks affinity prevents the scheduler to balance the load across
> + * the system.
> + */
> group_imbalanced,
> + /*
> + * The CPU is overloaded and can't provide expected CPU cycles to all
> + * tasks.
> + */
> group_overloaded
> };
Looks good.
>
> @@ -8563,7 +8586,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>
> /*
> * Try to use spare capacity of local group without overloading it or
> - * emptying busiest
> + * emptying busiest.
> + * XXX Spreading tasks across numa nodes is not always the best policy
> + * and special cares should be taken for SD_NUMA domain level before
> + * spreading the tasks. For now, load_balance() fully relies on
> + * NUMA_BALANCING and fbq_classify_group/rq to overide the decision.
> */
> if (local->group_type == group_has_spare) {
> if (busiest->group_type > group_fully_busy) {
Perfect. Any patch in that are can then update the comment and it
should be semi-obvious to the next reviewer that it's expected.
Thanks Vincent.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2019-11-08 18:37 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-18 13:26 [PATCH v4 00/10] sched/fair: rework the CFS load balance Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 01/11] sched/fair: clean up asym packing Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Clean " tip-bot2 for Vincent Guittot
2019-10-30 14:51 ` [PATCH v4 01/11] sched/fair: clean " Mel Gorman
2019-10-30 16:03 ` Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 02/11] sched/fair: rename sum_nr_running to sum_h_nr_running Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Rename sg_lb_stats::sum_nr_running " tip-bot2 for Vincent Guittot
2019-10-30 14:53 ` [PATCH v4 02/11] sched/fair: rename sum_nr_running " Mel Gorman
2019-10-18 13:26 ` [PATCH v4 03/11] sched/fair: remove meaningless imbalance calculation Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Remove " tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 04/11] sched/fair: rework load_balance Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Rework load_balance() tip-bot2 for Vincent Guittot
2019-10-30 15:45 ` [PATCH v4 04/11] sched/fair: rework load_balance Mel Gorman
2019-10-30 16:16 ` Valentin Schneider
2019-10-31 9:09 ` Vincent Guittot
2019-10-31 10:15 ` Mel Gorman
2019-10-31 11:13 ` Vincent Guittot
2019-10-31 11:40 ` Mel Gorman
2019-11-08 16:35 ` Vincent Guittot
2019-11-08 18:37 ` Mel Gorman [this message]
2019-11-12 10:58 ` Vincent Guittot
2019-11-12 15:06 ` Mel Gorman
2019-11-12 15:40 ` Vincent Guittot
2019-11-12 17:45 ` Mel Gorman
2019-11-18 13:50 ` Ingo Molnar
2019-11-18 13:57 ` Vincent Guittot
2019-11-18 14:51 ` Mel Gorman
2019-10-18 13:26 ` [PATCH v4 05/11] sched/fair: use rq->nr_running when balancing load Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use " tip-bot2 for Vincent Guittot
2019-10-30 15:54 ` [PATCH v4 05/11] sched/fair: use " Mel Gorman
2019-10-18 13:26 ` [PATCH v4 06/11] sched/fair: use load instead of runnable load in load_balance Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use load instead of runnable load in load_balance() tip-bot2 for Vincent Guittot
2019-10-30 15:58 ` [PATCH v4 06/11] sched/fair: use load instead of runnable load in load_balance Mel Gorman
2019-10-18 13:26 ` [PATCH v4 07/11] sched/fair: evenly spread tasks when not overloaded Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Spread out tasks evenly " tip-bot2 for Vincent Guittot
2019-10-30 16:03 ` [PATCH v4 07/11] sched/fair: evenly spread tasks " Mel Gorman
2019-10-18 13:26 ` [PATCH v4 08/11] sched/fair: use utilization to select misfit task Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use " tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 09/11] sched/fair: use load instead of runnable load in wakeup path Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Use " tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 10/11] sched/fair: optimize find_idlest_group Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Optimize find_idlest_group() tip-bot2 for Vincent Guittot
2019-10-18 13:26 ` [PATCH v4 11/11] sched/fair: rework find_idlest_group Vincent Guittot
2019-10-21 9:12 ` [tip: sched/core] sched/fair: Rework find_idlest_group() tip-bot2 for Vincent Guittot
2019-10-22 16:46 ` [PATCH] sched/fair: fix rework of find_idlest_group() Vincent Guittot
2019-10-23 7:50 ` Chen, Rong A
2019-10-30 16:07 ` Mel Gorman
2019-11-18 17:42 ` [tip: sched/core] sched/fair: Fix " tip-bot2 for Vincent Guittot
2019-11-22 14:37 ` [PATCH] sched/fair: fix " Valentin Schneider
2019-11-25 9:16 ` Vincent Guittot
2019-11-25 11:03 ` Valentin Schneider
2019-11-20 11:58 ` [PATCH v4 11/11] sched/fair: rework find_idlest_group Qais Yousef
2019-11-20 13:21 ` Vincent Guittot
2019-11-20 16:53 ` Vincent Guittot
2019-11-20 17:34 ` Qais Yousef
2019-11-20 17:43 ` Vincent Guittot
2019-11-20 18:10 ` Qais Yousef
2019-11-20 18:20 ` Vincent Guittot
2019-11-20 18:27 ` Qais Yousef
2019-11-20 19:28 ` Vincent Guittot
2019-11-20 19:55 ` Qais Yousef
2019-11-21 14:58 ` Qais Yousef
2019-11-22 14:34 ` Valentin Schneider
2019-11-25 9:59 ` Vincent Guittot
2019-11-25 11:13 ` Valentin Schneider
2019-10-21 7:50 ` [PATCH v4 00/10] sched/fair: rework the CFS load balance Ingo Molnar
2019-10-21 8:44 ` Vincent Guittot
2019-10-21 12:56 ` Phil Auld
2019-10-24 12:38 ` Phil Auld
2019-10-24 13:46 ` Phil Auld
2019-10-24 14:59 ` Vincent Guittot
2019-10-25 13:33 ` Phil Auld
2019-10-28 13:03 ` Vincent Guittot
2019-10-30 14:39 ` Phil Auld
2019-10-30 16:24 ` Dietmar Eggemann
2019-10-30 16:35 ` Valentin Schneider
2019-10-30 17:19 ` Phil Auld
2019-10-30 17:25 ` Valentin Schneider
2019-10-30 17:29 ` Phil Auld
2019-10-30 17:28 ` Vincent Guittot
2019-10-30 17:44 ` Phil Auld
2019-10-30 17:25 ` Vincent Guittot
2019-10-31 13:57 ` Phil Auld
2019-10-31 16:41 ` Vincent Guittot
2019-10-30 16:24 ` Mel Gorman
2019-10-30 16:35 ` Vincent Guittot
2019-11-18 13:15 ` Ingo Molnar
2019-11-25 12:48 ` Valentin Schneider
2020-01-03 16:39 ` Valentin Schneider
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