From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Valentin Schneider <valentin.schneider@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 9/9] sched/topology: Define and use shortcut pointers for wakeup sd_flag scan
Date: Thu, 16 Apr 2020 15:04:22 +0200 [thread overview]
Message-ID: <d508a6a5-c04f-087f-8767-6fb397b70055@arm.com> (raw)
In-Reply-To: <jhj4ktjpw2z.mognet@arm.com>
On 16.04.20 12:24, Valentin Schneider wrote:
>
> On 16/04/20 08:46, Vincent Guittot wrote:
>>> @@ -6657,7 +6646,19 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
>>>
>>> rcu_read_lock();
>>>
>>> - sd = highest_flag_domain(cpu, sd_flag);
>>> + switch (wake_flags & (WF_TTWU | WF_FORK | WF_EXEC)) {
>>> + case WF_TTWU:
>>> + sd_flag = SD_BALANCE_WAKE;
>>> + sd = rcu_dereference(per_cpu(sd_balance_wake, cpu));
>>
>> It's worth having a direct pointer for the fast path which we always
>> try to keep short but the other paths are already slow and will not
>> get any benefit of this per cpu pointer.
>> We should keep the loop for the slow paths
>>
>
> Which fast/slow paths are you referring to here? want_affine vs
> !want_affine? If so, do you then mean that we should do the switch case
> only when !want_affine, and otherwise look for the domain via the
> for_each_domain() loop?
Coming back to the v2 discussion on this patch
https://lore.kernel.org/r/20200311181601.18314-10-valentin.schneider@arm.com
SD_BALANCE_WAKE is not used in mainline anymore, so wakeups are always
fast today.
I.e. you wouldn't need a per_cpu(sd_balance_wake, cpu) since it's always
NULL.
I.e. want_affine logic and the 'for_each_domain(cpu, tmp)' isn't needed
anymore.
This will dramatically simplify the code in select_task_rq_fair().
But I guess Vincent wants to keep the functionality so we're able to
enable SD_BALANCE_WAKE on certain sd's?
next prev parent reply other threads:[~2020-04-16 13:04 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-15 21:05 [PATCH v3 0/9] sched: Streamline select_task_rq() & select_task_rq_fair() Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 1/9] sched/fair: find_idlest_group(): Remove unused sd_flag parameter Valentin Schneider
2020-04-16 7:40 ` Vincent Guittot
2020-05-01 18:22 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 2/9] sched/debug: Make sd->flags sysctl read-only Valentin Schneider
2020-05-01 18:22 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 3/9] sched: Remove checks against SD_LOAD_BALANCE Valentin Schneider
2020-05-01 18:22 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 4/9] sched/topology: Kill SD_LOAD_BALANCE Valentin Schneider
2020-05-01 18:22 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 5/9] sched: Add WF_TTWU, WF_EXEC wakeup flags Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 6/9] sched: Kill select_task_rq()'s sd_flag parameter Valentin Schneider
2020-04-16 7:42 ` Vincent Guittot
2020-04-16 10:24 ` Valentin Schneider
2020-04-16 10:47 ` Peter Zijlstra
2020-04-16 11:43 ` Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 7/9] sched/fair: Dissociate wakeup decisions from SD flag value Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 8/9] sched/fair: Split select_task_rq_fair want_affine logic Valentin Schneider
2020-04-15 21:05 ` [PATCH v3 9/9] sched/topology: Define and use shortcut pointers for wakeup sd_flag scan Valentin Schneider
2020-04-16 7:46 ` Vincent Guittot
2020-04-16 10:24 ` Valentin Schneider
2020-04-16 13:04 ` Dietmar Eggemann [this message]
2020-04-16 13:36 ` Vincent Guittot
2020-04-16 15:27 ` Valentin Schneider
2020-04-16 15:58 ` Vincent Guittot
2020-04-16 20:54 ` Valentin Schneider
2020-04-16 10:58 ` [PATCH v3 0/9] sched: Streamline select_task_rq() & select_task_rq_fair() Peter Zijlstra
2020-04-16 11:00 ` Peter Zijlstra
2020-04-16 11:02 ` Valentin Schneider
2020-04-16 13:00 ` Vincent Guittot
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=d508a6a5-c04f-087f-8767-6fb397b70055@arm.com \
--to=dietmar.eggemann@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=valentin.schneider@arm.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
all inboxes | Powered by JetHome®