From: Valentin Schneider <valentin.schneider@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
Quentin Perret <qperret@google.com>,
Pavan Kondeti <pkondeti@codeaurora.org>,
Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH 1/8] sched/fair: Clean up active balance nr_balance_failed trickery
Date: Fri, 05 Feb 2021 14:05:35 +0000 [thread overview]
Message-ID: <jhjy2g21ufk.mognet@arm.com> (raw)
In-Reply-To: <CAKfTPtDrKrkZBQuaFSGvRo=aQAdF0vugxWervQpWeza21XL=yw@mail.gmail.com>
On 05/02/21 14:51, Vincent Guittot wrote:
> On Thu, 28 Jan 2021 at 19:32, Valentin Schneider
> <valentin.schneider@arm.com> wrote:
>>
>> When triggering an active load balance, sd->nr_balance_failed is set to
>> such a value that any further can_migrate_task() using said sd will ignore
>> the output of task_hot().
>>
>> This behaviour makes sense, as active load balance intentionally preempts a
>> rq's running task to migrate it right away, but this asynchronous write is
>> a bit shoddy, as the stopper thread might run active_load_balance_cpu_stop
>> before the sd->nr_balance_failed write either becomes visible to the
>> stopper's CPU or even happens on the CPU that appended the stopper work.
>>
>> Add a struct lb_env flag to denote active balancing, and use it in
>> can_migrate_task(). Remove the sd->nr_balance_failed write that served the
>> same purpose.
>>
>> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
>> ---
>> kernel/sched/fair.c | 17 ++++++++++-------
>> 1 file changed, 10 insertions(+), 7 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 197a51473e0c..0f6a4e58ce3c 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -7423,6 +7423,7 @@ enum migration_type {
>> #define LBF_SOME_PINNED 0x08
>> #define LBF_NOHZ_STATS 0x10
>> #define LBF_NOHZ_AGAIN 0x20
>> +#define LBF_ACTIVE_LB 0x40
>>
>> struct lb_env {
>> struct sched_domain *sd;
>> @@ -7608,10 +7609,14 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>>
>> /*
>> * Aggressive migration if:
>> - * 1) destination numa is preferred
>> - * 2) task is cache cold, or
>> - * 3) too many balance attempts have failed.
>> + * 1) active balance
>> + * 2) destination numa is preferred
>> + * 3) task is cache cold, or
>> + * 4) too many balance attempts have failed.
>> */
>> + if (env->flags & LBF_ACTIVE_LB)
>> + return 1;
>> +
>
> This changes the behavior for numa system because it skips
> migrate_degrades_locality() which can return 1 and prevent active
> migration whatever nr_balance_failed
>
> Is that intentional ?
>
If I read this right, the result of migrate_degrades_locality() is
(currently) ignored if
env->sd->nr_balance_failed > env->sd->cache_nice_tries
While on the load_balance() side, we have:
/* We've kicked active balancing, force task migration. */
sd->nr_balance_failed = sd->cache_nice_tries+1;
So we should currently be ignoring migrate_degrades_locality() in the
active balance case - what I wrote in the changelog for task_hot() still
applies to migrate_degrades_locality().
next prev parent reply other threads:[~2021-02-05 23:31 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 18:31 [PATCH 0/8] sched/fair: misfit task load-balance tweaks Valentin Schneider
2021-01-28 18:31 ` [PATCH 1/8] sched/fair: Clean up active balance nr_balance_failed trickery Valentin Schneider
2021-02-03 15:14 ` Qais Yousef
2021-02-03 18:42 ` Valentin Schneider
2021-02-04 15:05 ` Qais Yousef
2021-02-05 13:51 ` Vincent Guittot
2021-02-05 14:05 ` Valentin Schneider [this message]
2021-02-05 14:34 ` Vincent Guittot
2021-01-28 18:31 ` [PATCH 2/8] sched/fair: Add more sched_asym_cpucapacity static branch checks Valentin Schneider
2021-02-03 15:14 ` Qais Yousef
2021-02-09 8:42 ` Vincent Guittot
2021-01-28 18:31 ` [PATCH 3/8] sched/fair: Tweak misfit-related capacity checks Valentin Schneider
2021-02-03 15:15 ` Qais Yousef
2021-02-03 18:42 ` Valentin Schneider
2021-02-05 14:31 ` Vincent Guittot
2021-02-05 16:59 ` Valentin Schneider
2021-02-05 17:17 ` Vincent Guittot
2021-02-05 20:07 ` Valentin Schneider
2021-02-08 15:29 ` Vincent Guittot
2021-02-08 17:49 ` Valentin Schneider
2021-01-28 18:31 ` [PATCH 4/8] sched/fair: Use dst_cpu's capacity rather than group {min, max} capacity Valentin Schneider
2021-02-03 15:15 ` Qais Yousef
2021-01-28 18:31 ` [PATCH 5/8] sched/fair: Make check_misfit_status() only compare dynamic capacities Valentin Schneider
2021-02-03 15:15 ` Qais Yousef
2021-02-04 10:49 ` Dietmar Eggemann
2021-02-04 11:34 ` Valentin Schneider
2021-02-04 14:57 ` Dietmar Eggemann
2021-01-28 18:31 ` [PATCH 6/8] sched/fair: Filter out locally-unsolvable misfit imbalances Valentin Schneider
2021-02-03 15:16 ` Qais Yousef
2021-02-03 18:43 ` Valentin Schneider
2021-01-28 18:31 ` [PATCH 7/8] sched/fair: Attempt misfit active balance when migration_type != migrate_misfit Valentin Schneider
2021-02-03 15:16 ` Qais Yousef
2021-02-03 18:43 ` Valentin Schneider
2021-02-04 11:44 ` Dietmar Eggemann
2021-02-04 12:22 ` Valentin Schneider
2021-02-09 8:58 ` Vincent Guittot
2021-02-09 18:19 ` Valentin Schneider
2021-01-28 18:31 ` [PATCH 8/8] sched/fair: Relax task_hot() for misfit tasks Valentin Schneider
2021-02-03 15:17 ` Qais Yousef
2021-02-08 16:21 ` Vincent Guittot
2021-02-08 18:24 ` Valentin Schneider
2021-02-09 8:56 ` Vincent Guittot
2021-02-03 15:14 ` [PATCH 0/8] sched/fair: misfit task load-balance tweaks Qais Yousef
2021-02-03 18:43 ` Valentin Schneider
2021-02-04 12:03 ` Dietmar Eggemann
2021-02-04 12:36 ` Valentin Schneider
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=jhjy2g21ufk.mognet@arm.com \
--to=valentin.schneider@arm.com \
--cc=dietmar.eggemann@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=morten.rasmussen@arm.com \
--cc=peterz@infradead.org \
--cc=pkondeti@codeaurora.org \
--cc=qais.yousef@arm.com \
--cc=qperret@google.com \
--cc=riel@surriel.com \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).