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From: Valentin Schneider <valentin.schneider@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Phil Auld <pauld@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	Quentin Perret <quentin.perret@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 00/10] sched/fair: rework the CFS load balance
Date: Wed, 30 Oct 2019 17:35:55 +0100	[thread overview]
Message-ID: <bf96be8a-2358-b9ab-b8eb-d0b8b94ed0d7@arm.com> (raw)
In-Reply-To: <564ca629-5c34-dbd1-8e64-2da6910b18a3@arm.com>



On 30/10/2019 17:24, Dietmar Eggemann wrote:
> On 30.10.19 15:39, Phil Auld wrote:
>> Hi Vincent,
>>
>> On Mon, Oct 28, 2019 at 02:03:15PM +0100 Vincent Guittot wrote:
> 
> [...]
> 
>>>> When you say slow versus fast wakeup paths what do you mean? I'm still
>>>> learning my way around all this code.
>>>
>>> When task wakes up, we can decide to
>>> - speedup the wakeup and shorten the list of cpus and compare only
>>> prev_cpu vs this_cpu (in fact the group of cpu that share their
>>> respective LLC). That's the fast wakeup path that is used most of the
>>> time during a wakeup
>>> - or start to find the idlest CPU of the system and scan all domains.
>>> That's the slow path that is used for new tasks or when a task wakes
>>> up a lot of other tasks at the same time
> 
> [...]
> 
> Is the latter related to wake_wide()? If yes, is the SD_BALANCE_WAKE
> flag set on the sched domains on your machines? IMHO, otherwise those
> wakeups are not forced into the slowpath (if (unlikely(sd))?
> 
> I had this discussion the other day with Valentin S. on #sched and we
> were not sure how SD_BALANCE_WAKE is set on sched domains on
> !SD_ASYM_CPUCAPACITY systems.
> 

Well from the code nobody but us (asymmetric capacity systems) set
SD_BALANCE_WAKE. I was however curious if there were some folks who set it
with out of tree code for some reason.

As Dietmar said, not having SD_BALANCE_WAKE means you'll never go through
the slow path on wakeups, because there is no domain with SD_BALANCE_WAKE for
the domain loop to find. Depending on your topology you most likely will
go through it on fork or exec though.

IOW wake_wide() is not really widening the wakeup scan on wakeups using
mainline topology code (disregarding asymmetric capacity systems), which
sounds a bit... off.

  reply	other threads:[~2019-10-30 16:36 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
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 [this message]
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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