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From: Qais Yousef <qais.yousef@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>, mark.rutland@arm.com
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 11/11] sched/fair: rework find_idlest_group
Date: Thu, 21 Nov 2019 14:58:09 +0000	[thread overview]
Message-ID: <20191121145808.vlixdy3ilxfaswyr@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20191120195521.nvhzvd3x7l7jdxsr@e107158-lin.cambridge.arm.com>

On 11/20/19 19:55, Qais Yousef wrote:
> On 11/20/19 20:28, Vincent Guittot wrote:
> > I run few more tests and i can get either hw counter with 0 or not.
> > The main difference is on which CPU it runs: either big or little
> > little return always 0 and big always non-zero value
> > 
> > on v5.4-rc7 and tip/sched/core, cpu0-3 return 0 and other non zeroa
> > but on next, it's the opposite cpu0-3 return non zero ratio
> > 
> > Could you try to run the test with taskset to run it on big or little ?
> 
> Nice catch!
> 
> Yes indeed using taskset and forcing it to run on the big cpus it passes even
> on linux-next/next-20191119.
> 
> So the relation to your patch is that it just biased where this test is likely
> to run in my case and highlighted the breakage in the counters, probably?
> 
> FWIW, if I use taskset to force always big it passes. Always small, the counters
> are always 0 and it passes too. But if I have mixed I see what I pasted before,
> the counters have valid value but nhw is 0.
> 
> So the questions are, why little counters aren't working. And whether we should
> run the test with taskset generally as it can't handle the asymmetry correctly.
> 
> Let me first try to find out why the little counters aren't working.

So it turns out there's a caveat on usage of perf counters on big.LITTLE
systems.

Mark on CC can explain this better than me so I'll leave the details to him.

Sorry about the noise Vincent - it seems your patch was shifting things
slightly to cause migrating the task to another CPU, hence trigger the failure
on reading the perf counters, and the test in return.

Thanks

--
Qais Yousef

  reply	other threads:[~2019-11-21 14:58 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
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 [this message]
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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