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From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Rik van Riel <riel@surriel.com>, linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com, pjt@google.com, peterz@infradead.org,
	mingo@redhat.com, morten.rasmussen@arm.com, tglx@linutronix.de,
	mgorman@techsingularity.net, vincent.guittot@linaro.org
Subject: Re: [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues
Date: Mon, 2 Sep 2019 12:53:48 +0200	[thread overview]
Message-ID: <94ba95b9-9cfe-d715-dded-ff92700d47eb@arm.com> (raw)
In-Reply-To: <20190822021740.15554-1-riel@surriel.com>

On 22/08/2019 04:17, Rik van Riel wrote:
> The current implementation of the CPU controller uses hierarchical
> runqueues, where on wakeup a task is enqueued on its group's runqueue,
> the group is enqueued on the runqueue of the group above it, etc.
> 
> This increases a fairly large amount of overhead for workloads that
> do a lot of wakeups a second, especially given that the default systemd
> hierarchy is 2 or 3 levels deep.
> 
> This patch series is an attempt at reducing that overhead, by placing
> all the tasks on the same runqueue, and scaling the task priority by
> the priority of the group, which is calculated periodically.
> 
> My main TODO items for the next period of time are likely going to
> be testing, testing, and testing. I hope to find and flush out any
> corner case I can find, and make sure performance does not regress
> with any workloads, and hopefully improves some.

I did some testing with a small & simple rt-app based test-case:

2 CPUs (rq->cpu_capacity_orig=1024), CPUfreq performance governor

2 taskgroups /tg0 and /tg1

6 CFS tasks (periodic, 8/16ms (runtime/period))

/tg0 (cpu.shares=1024) ran 4 tasks and /tg1 (cpu.shares=1024) ran 2 tasks

(arm64 defconfig with !CONFIG_NUMA_BALANCING, !CONFIG_SCHED_AUTOGROUP)

---

v5.2:

The 2 /tg1 tasks ran 8/16ms. The 4 /tg0 tasks ran 4/16ms in the
beginning and then 8/16ms after the 2 /tg1 tasks did finish.

---

v5.2 + v4:

There is no runtime/period pattern visible anymore. I see a lot of extra
wakeup latency for those tasks though.

v5.2 + (v4 without 07/15, 08/15, 15/15) didn't change much.

---

I could try to reduce the stack even further (e.g. without 13/15).

IMHO it's a good idea to have a set of these small & simple test-cases
handy to verify that the base-functionality is still in place. This
might be hard to achieve with benchmarks.

  parent reply	other threads:[~2019-09-02 10:53 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-22  2:17 [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues Rik van Riel
2019-08-22  2:17 ` [PATCH 01/15] sched: introduce task_se_h_load helper Rik van Riel
2019-08-23 18:13   ` Dietmar Eggemann
2019-08-24  0:05     ` Rik van Riel
2019-08-22  2:17 ` [PATCH 02/15] sched: change /proc/sched_debug fields Rik van Riel
2019-08-22  2:17 ` [PATCH 03/15] sched,fair: redefine runnable_load_avg as the sum of task_h_load Rik van Riel
2019-08-28 13:50   ` Vincent Guittot
2019-08-28 14:47     ` Rik van Riel
2019-08-28 15:02       ` Vincent Guittot
2019-08-22  2:17 ` [PATCH 04/15] sched,fair: move runnable_load_avg to cfs_rq Rik van Riel
2019-08-22  2:17 ` [PATCH 05/15] sched,fair: remove cfs_rqs from leaf_cfs_rq_list bottom up Rik van Riel
2019-08-28 14:09   ` Vincent Guittot
2019-08-22  2:17 ` [PATCH 06/15] sched,cfs: use explicit cfs_rq of parent se helper Rik van Riel
2019-08-28 13:53   ` Vincent Guittot
2019-08-28 15:28     ` Rik van Riel
2019-08-28 16:34       ` Vincent Guittot
2019-08-22  2:17 ` [PATCH 07/15] sched,cfs: fix zero length timeslice calculation Rik van Riel
2019-08-28 16:59   ` Vincent Guittot
2019-08-22  2:17 ` [PATCH 08/15] sched,fair: simplify timeslice length code Rik van Riel
2019-08-28 17:32   ` Vincent Guittot
2019-08-28 23:18     ` Rik van Riel
2019-08-29 14:02       ` Vincent Guittot
2019-08-29 16:00         ` Rik van Riel
2019-08-30  6:41           ` Vincent Guittot
2019-08-30 15:01             ` Rik van Riel
2019-09-02  7:51               ` Vincent Guittot
2019-09-02 17:47                 ` Rik van Riel
2019-08-22  2:17 ` [PATCH 09/15] sched,fair: refactor enqueue/dequeue_entity Rik van Riel
2019-09-03 15:38   ` Vincent Guittot
2019-09-03 20:27     ` Rik van Riel
2019-09-04  6:44       ` Vincent Guittot
2019-08-22  2:17 ` [PATCH 10/15] sched,fair: add helper functions for flattened runqueue Rik van Riel
2019-08-22  2:17 ` [PATCH 11/15] sched,fair: flatten hierarchical runqueues Rik van Riel
2019-08-23 18:14   ` Dietmar Eggemann
2019-08-24  1:16     ` Rik van Riel
2019-08-22  2:17 ` [PATCH 12/15] sched,fair: flatten update_curr functionality Rik van Riel
2019-08-27 10:37   ` Dietmar Eggemann
2019-08-22  2:17 ` [PATCH 13/15] sched,fair: propagate sum_exec_runtime up the hierarchy Rik van Riel
2019-08-28  7:51   ` Dietmar Eggemann
2019-08-28 13:14     ` Rik van Riel
2019-08-29 17:20       ` Dietmar Eggemann
2019-08-29 18:06         ` Rik van Riel
2019-08-22  2:17 ` [PATCH 14/15] sched,fair: ramp up task_se_h_weight quickly Rik van Riel
2019-08-22  2:17 ` [PATCH 15/15] sched,fair: scale vdiff in wakeup_preempt_entity Rik van Riel
2019-09-02 10:53 ` Dietmar Eggemann [this message]
2019-09-03  1:44   ` [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues Rik van Riel

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