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From: Tim Chen <tim.c.chen@linux.intel.com>
To: Dario Faggioli <dfaggioli@suse.com>,
	Julien Desfossez <jdesfossez@digitalocean.com>,
	"Li, Aubrey" <aubrey.li@linux.intel.com>
Cc: "Aaron Lu" <aaron.lu@linux.alibaba.com>,
	"Aubrey Li" <aubrey.intel@gmail.com>,
	"Subhra Mazumdar" <subhra.mazumdar@oracle.com>,
	"Vineeth Remanan Pillai" <vpillai@digitalocean.com>,
	"Nishanth Aravamudan" <naravamudan@digitalocean.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Paul Turner" <pjt@google.com>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Linux List Kernel Mailing" <linux-kernel@vger.kernel.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Greg Kerr" <kerrnel@google.com>, "Phil Auld" <pauld@redhat.com>,
	"Valentin Schneider" <valentin.schneider@arm.com>,
	"Mel Gorman" <mgorman@techsingularity.net>,
	"Pawan Gupta" <pawan.kumar.gupta@linux.intel.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3
Date: Wed, 7 Aug 2019 10:10:47 -0700	[thread overview]
Message-ID: <69cd9bca-da28-1d35-3913-1efefe0c1c22@linux.intel.com> (raw)
In-Reply-To: <eec72c2d533b7600c63de3c8001cc6ab9e915afe.camel@suse.com>

On 8/7/19 1:58 AM, Dario Faggioli wrote:

> So, here comes my question: I've done a benchmarking campaign (yes,
> I'll post numbers soon) using this branch:
> 
> https://github.com/digitalocean/linux-coresched.git  vpillai/coresched-v3-v5.1.5-test
> https://github.com/digitalocean/linux-coresched/tree/vpillai/coresched-v3-v5.1.5-test
> 
> Last commit:
> 7feb1007f274 "Fix stalling of untagged processes competing with tagged
> processes"
> 
> Since I see that, in this thread, there are various patches being
> proposed and discussed... should I rerun my benchmarks with them
> applied? If yes, which ones? And is there, by any chance, one (or maybe
> more than one) updated git branch(es)?
> 
> Thanks in advance and Regards
> 

Hi Dario,

Having an extra set of eyes are certainly welcomed.
I'll give my 2 cents on the issues with v3.
Others feel free to chime in if my understanding is
incorrect or I'm missing something.

1) Unfairness between the sibling threads
-----------------------------------------
One sibling thread could be suppressing and force idling
the sibling thread over proportionally.  Resulting in
the force idled CPU not getting run and stall tasks on
suppressed CPU.

Status:
i) Aaron has proposed a patchset here based on using one
rq as a base reference for vruntime for task priority
comparison between siblings.

https://lore.kernel.org/lkml/20190725143248.GC992@aaronlu/
It works well on fairness but has some initialization issues

ii) Tim has proposed a patchset here to account for forced
idle time in rq's min_vruntime
https://lore.kernel.org/lkml/f96350c1-25a9-0564-ff46-6658e96d726c@linux.intel.com/
It improves over v3 with simpler logic compared to
Aaron's patch, but does not work as well on fairness

iii) Tim has proposed yet another patch to maintain fairness
of forced idle time between CPU threads per Peter's suggestion.
https://lore.kernel.org/lkml/21933a50-f796-3d28-664c-030cb7c98431@linux.intel.com/
Its performance has yet to be tested.

2) Not rescheduling forced idled CPU
------------------------------------
The forced idled CPU does not get a chance to re-schedule
itself, and will stall for a long time even though it
has eligible tasks to run.

Status:
i) Aaron proposed a patch to fix this to check if there
are runnable tasks when scheduling tick comes in.
https://lore.kernel.org/lkml/20190725143344.GD992@aaronlu/

ii) Vineeth has patches to this issue and also issue 1, based
on scheduling in a new "forced idle task" when getting forced
idle, but has yet to post the patches.

3) Load balancing between CPU cores
-----------------------------------
Say if one CPU core's sibling threads get forced idled
a lot as it has mostly incompatible tasks between the siblings,
moving the incompatible load to other cores and pulling
compatible load to the core could help CPU utilization.

So just considering the load of a task is not enough during
load balancing, task compatibility also needs to be considered.
Peter has put in mechanisms to balance compatible tasks between
CPU thread siblings, but not across cores.

Status:
I have not seen patches on this issue.  This issue could lead to
large variance in workload performance based on your luck
in placing the workload among the cores.

Thanks.

Tim

  reply	other threads:[~2019-08-07 17:10 UTC|newest]

Thread overview: 161+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 20:36 Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 01/16] stop_machine: Fix stop_cpus_in_progress ordering Vineeth Remanan Pillai
2019-08-08 10:54   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 16:19   ` [RFC PATCH v3 01/16] " mark gross
2019-08-26 16:59     ` Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 02/16] sched: Fix kerneldoc comment for ia64_set_curr_task Vineeth Remanan Pillai
2019-08-08 10:55   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 16:20   ` [RFC PATCH v3 02/16] " mark gross
2019-05-29 20:36 ` [RFC PATCH v3 03/16] sched: Wrap rq::lock access Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 04/16] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Vineeth Remanan Pillai
2019-08-08 10:55   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 05/16] sched: Add task_struct pointer to sched_class::set_curr_task Vineeth Remanan Pillai
2019-08-08 10:57   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 06/16] sched/fair: Export newidle_balance() Vineeth Remanan Pillai
2019-08-08 10:58   ` [tip:sched/core] sched/fair: Expose newidle_balance() tip-bot for Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 07/16] sched: Allow put_prev_task() to drop rq->lock Vineeth Remanan Pillai
2019-08-08 10:58   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 16:51   ` [RFC PATCH v3 07/16] " mark gross
2019-05-29 20:36 ` [RFC PATCH v3 08/16] sched: Rework pick_next_task() slow-path Vineeth Remanan Pillai
2019-08-08 10:59   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 17:01   ` [RFC PATCH v3 08/16] " mark gross
2019-05-29 20:36 ` [RFC PATCH v3 09/16] sched: Introduce sched_class::pick_task() Vineeth Remanan Pillai
2019-08-26 17:14   ` mark gross
2019-05-29 20:36 ` [RFC PATCH v3 10/16] sched: Core-wide rq->lock Vineeth Remanan Pillai
2019-05-31 11:08   ` Peter Zijlstra
2019-05-31 15:23     ` Vineeth Pillai
2019-05-29 20:36 ` [RFC PATCH v3 11/16] sched: Basic tracking of matching tasks Vineeth Remanan Pillai
2019-08-26 20:59   ` mark gross
2019-05-29 20:36 ` [RFC PATCH v3 12/16] sched: A quick and dirty cgroup tagging interface Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 13/16] sched: Add core wide task selection and scheduling Vineeth Remanan Pillai
2019-06-07 23:36   ` Pawan Gupta
2019-05-29 20:36 ` [RFC PATCH v3 14/16] sched/fair: Add a few assertions Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 15/16] sched: Trivial forced-newidle balancer Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 16/16] sched: Debug bits Vineeth Remanan Pillai
2019-05-29 21:02   ` Peter Oskolkov
2019-05-30 14:04 ` [RFC PATCH v3 00/16] Core scheduling v3 Aubrey Li
2019-05-30 14:17   ` Julien Desfossez
2019-05-31  4:55     ` Aubrey Li
2019-05-31  3:01   ` Aaron Lu
2019-05-31  5:12     ` Aubrey Li
2019-05-31  6:09       ` Aaron Lu
2019-05-31  6:53         ` Aubrey Li
2019-05-31  7:44           ` Aaron Lu
2019-05-31  8:26             ` Aubrey Li
2019-05-31 21:08     ` Julien Desfossez
2019-06-06 15:26       ` Julien Desfossez
2019-06-12  1:52         ` Li, Aubrey
2019-06-12 16:06           ` Julien Desfossez
2019-06-12 16:33         ` Julien Desfossez
2019-06-13  0:03           ` Subhra Mazumdar
2019-06-13  3:22             ` Julien Desfossez
2019-06-17  2:51               ` Aubrey Li
2019-06-19 18:33                 ` Julien Desfossez
2019-07-18 10:07                   ` Aaron Lu
2019-07-18 23:27                     ` Tim Chen
2019-07-19  5:52                       ` Aaron Lu
2019-07-19 11:48                         ` Aubrey Li
2019-07-19 18:33                         ` Tim Chen
2019-07-22 10:26                     ` Aubrey Li
2019-07-22 10:43                       ` Aaron Lu
2019-07-23  2:52                         ` Aubrey Li
2019-07-25 14:30                       ` Aaron Lu
2019-07-25 14:31                         ` [RFC PATCH 1/3] wrapper for cfs_rq->min_vruntime Aaron Lu
2019-07-25 14:32                         ` [PATCH 2/3] core vruntime comparison Aaron Lu
2019-08-06 14:17                           ` Peter Zijlstra
2019-07-25 14:33                         ` [PATCH 3/3] temp hack to make tick based schedule happen Aaron Lu
2019-07-25 21:42                         ` [RFC PATCH v3 00/16] Core scheduling v3 Li, Aubrey
2019-07-26 15:21                         ` Julien Desfossez
2019-07-26 21:29                           ` Tim Chen
2019-07-31  2:42                           ` Li, Aubrey
2019-08-02 15:37                             ` Julien Desfossez
2019-08-05 15:55                               ` Tim Chen
2019-08-06  3:24                                 ` Aaron Lu
2019-08-06  6:56                                   ` Aubrey Li
2019-08-06  7:04                                     ` Aaron Lu
2019-08-06 12:24                                       ` Vineeth Remanan Pillai
2019-08-06 13:49                                         ` Aaron Lu
2019-08-06 16:14                                           ` Vineeth Remanan Pillai
2019-08-06 14:16                                         ` Peter Zijlstra
2019-08-06 15:53                                           ` Vineeth Remanan Pillai
2019-08-06 17:03                                   ` Tim Chen
2019-08-06 17:12                                     ` Peter Zijlstra
2019-08-06 21:19                                       ` Tim Chen
2019-08-08  6:47                                         ` Aaron Lu
2019-08-08 17:27                                           ` Tim Chen
2019-08-08 21:42                                             ` Tim Chen
2019-08-10 14:15                                               ` Aaron Lu
2019-08-12 15:38                                                 ` Vineeth Remanan Pillai
2019-08-13  2:24                                                   ` Aaron Lu
2019-08-08 12:55                                 ` Aaron Lu
2019-08-08 16:39                                   ` Tim Chen
2019-08-10 14:18                                     ` Aaron Lu
2019-08-05 20:09                               ` Phil Auld
2019-08-06 13:54                                 ` Aaron Lu
2019-08-06 14:17                                   ` Phil Auld
2019-08-06 14:41                                     ` Aaron Lu
2019-08-06 14:55                                       ` Phil Auld
2019-08-07  8:58                               ` Dario Faggioli
2019-08-07 17:10                                 ` Tim Chen [this message]
2019-08-15 16:09                                   ` Dario Faggioli
2019-08-16  2:33                                     ` Aaron Lu
2019-09-05  1:44                                   ` Julien Desfossez
2019-09-06 22:17                                     ` Tim Chen
2019-09-18 21:27                                     ` Tim Chen
2019-09-06 18:30                                   ` Tim Chen
2019-09-11 14:02                                     ` Aaron Lu
2019-09-11 16:19                                       ` Tim Chen
2019-09-11 16:47                                         ` Vineeth Remanan Pillai
2019-09-12 12:35                                           ` Aaron Lu
2019-09-12 17:29                                             ` Tim Chen
2019-09-13 14:15                                               ` Aaron Lu
2019-09-13 17:13                                                 ` Tim Chen
2019-09-30 11:53                                             ` Vineeth Remanan Pillai
2019-10-02 20:48                                               ` Vineeth Remanan Pillai
2019-10-10 13:54                                                 ` Aaron Lu
2019-10-10 14:29                                                   ` Vineeth Remanan Pillai
2019-10-11  7:33                                                     ` Aaron Lu
2019-10-11 11:32                                                       ` Vineeth Remanan Pillai
2019-10-11 12:01                                                         ` Aaron Lu
2019-10-11 12:10                                                           ` Vineeth Remanan Pillai
2019-10-12  3:55                                                             ` Aaron Lu
2019-10-13 12:44                                                               ` Vineeth Remanan Pillai
2019-10-14  9:57                                                                 ` Aaron Lu
2019-10-21 12:30                                                                   ` Vineeth Remanan Pillai
2019-09-12 12:04                                         ` Aaron Lu
2019-09-12 17:05                                           ` Tim Chen
2019-09-13 13:57                                             ` Aaron Lu
2019-09-12 23:12                                           ` Aubrey Li
2019-09-15 14:14                                             ` Aaron Lu
2019-09-18  1:33                                               ` Aubrey Li
2019-09-18 20:40                                                 ` Tim Chen
2019-09-18 22:16                                                   ` Aubrey Li
2019-09-30 14:36                                                     ` Vineeth Remanan Pillai
2019-10-29 20:40                                                   ` Julien Desfossez
2019-11-01 21:42                                                     ` Tim Chen
2019-10-29  9:11                                               ` Dario Faggioli
2019-10-29  9:15                                                 ` Dario Faggioli
2019-10-29  9:16                                                 ` Dario Faggioli
2019-10-29  9:17                                                 ` Dario Faggioli
2019-10-29  9:18                                                 ` Dario Faggioli
2019-10-29  9:18                                                 ` Dario Faggioli
2019-10-29  9:19                                                 ` Dario Faggioli
2019-10-29  9:20                                                 ` Dario Faggioli
2019-10-29 20:34                                                   ` Julien Desfossez
2019-11-15 16:30                                                     ` Dario Faggioli
2019-09-25  2:40                                     ` Aubrey Li
2019-09-25 17:24                                       ` Tim Chen
2019-09-25 22:07                                         ` Aubrey Li
2019-09-30 15:22                                     ` Julien Desfossez
2019-08-27 21:14 ` Matthew Garrett
2019-08-27 21:50   ` Peter Zijlstra
2019-08-28 15:30     ` Phil Auld
2019-08-28 16:01       ` Peter Zijlstra
2019-08-28 16:37         ` Tim Chen
2019-08-29 14:30         ` Phil Auld
2019-08-29 14:38           ` Peter Zijlstra
2019-09-10 14:27             ` Julien Desfossez
2019-09-18 21:12               ` Tim Chen
2019-08-28 15:59     ` Tim Chen
2019-08-28 16:16       ` Peter Zijlstra
2019-08-27 23:24   ` Aubrey Li

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