From: Valentin Schneider <valentin.schneider@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
peterz@infradead.org, vincent.guittot@linaro.org
Subject: Re: [PATCH v2 9/9] sched/topology: Define and use shortcut pointers for wakeup sd_flag scan
Date: Thu, 19 Mar 2020 12:22:34 +0000 [thread overview]
Message-ID: <jhj8sjwilf9.mognet@arm.com> (raw)
In-Reply-To: <53763a32-0ce5-e267-9d5d-99e65c921d08@arm.com>
On Thu, Mar 19 2020, Dietmar Eggemann wrote:
> On 11.03.20 19:16, Valentin Schneider wrote:
>> @@ -6621,7 +6610,19 @@ 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));
>
> IMHO, since we hard-code 0*SD_BALANCE_WAKE in sd_init(), sd would always
> be NULL, so !want_affine (i.e. wake_wide()) would still go sis().
>
> SD_BALANCE_WAKE is no a topology related sd_flag so it can't be set from
> outside. Since the sd->flags sysctl is now read-only, wouldn't this case
> be redundant?
>
On a purely mainline kernel, yes, 'sd' will always be NULL for
wakeups. I'm playing a bit more conservative here with SD_BALANCE_WAKE,
as I could see some folks using that flag in some ~franken~ downstream
kernels (I am not aware of any, however).
Also, to be fair we've only very recently gotten rid of the last
SD_BALANCE_WAKE user (asymmetric CPU capacity topologies), so I felt
like keeping it around for a bit before entirely killing it would be a
sane thing to do.
> [...]
prev parent reply other threads:[~2020-03-19 12:23 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-11 18:15 [PATCH v2 0/9] sched: Streamline select_task_rq() & select_task_rq_fair() Valentin Schneider
2020-03-11 18:15 ` [PATCH v2 1/9] sched/fair: find_idlest_group(): Remove unused sd_flag parameter Valentin Schneider
2020-03-19 9:05 ` Dietmar Eggemann
2020-03-11 18:15 ` [PATCH v2 2/9] sched/debug: Make sd->flags sysctl read-only Valentin Schneider
2020-03-19 9:07 ` Dietmar Eggemann
2020-03-19 12:04 ` Valentin Schneider
2020-03-11 18:15 ` [PATCH v2 3/9] sched: Remove checks against SD_LOAD_BALANCE Valentin Schneider
2020-03-19 10:28 ` Dietmar Eggemann
2020-03-19 12:05 ` Valentin Schneider
2020-03-23 14:26 ` Dietmar Eggemann
2020-03-23 17:17 ` Valentin Schneider
2020-03-11 18:15 ` [PATCH v2 4/9] sched/topology: Kill SD_LOAD_BALANCE Valentin Schneider
2020-03-19 10:29 ` Dietmar Eggemann
2020-03-19 12:06 ` Valentin Schneider
2020-03-11 18:15 ` [PATCH v2 5/9] sched: Add WF_TTWU, WF_EXEC wakeup flags Valentin Schneider
2020-03-11 18:15 ` [PATCH v2 6/9] sched: Kill select_task_rq()'s sd_flag parameter Valentin Schneider
2020-03-11 18:15 ` [PATCH v2 7/9] sched/fair: Dissociate wakeup decisions from SD flag value Valentin Schneider
2020-03-11 18:16 ` [PATCH v2 8/9] sched/fair: Split select_task_rq_fair want_affine logic Valentin Schneider
2020-03-19 10:30 ` Dietmar Eggemann
2020-03-19 12:06 ` Valentin Schneider
2020-03-11 18:16 ` [PATCH v2 9/9] sched/topology: Define and use shortcut pointers for wakeup sd_flag scan Valentin Schneider
2020-03-19 10:46 ` Dietmar Eggemann
2020-03-19 12:22 ` Valentin Schneider [this message]
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=jhj8sjwilf9.mognet@arm.com \
--to=valentin.schneider@arm.com \
--cc=dietmar.eggemann@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.