From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rjw@rjwysocki.net, oleg@redhat.com, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de,
ebiederm@xmission.com, bigeasy@linutronix.de,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org, tj@kernel.org,
linux-pm@vger.kernel.org
Subject: Re: [PATCH v3 3/6] sched: Change wait_task_inactive()s match_state
Date: Sun, 4 Sep 2022 12:44:36 +0200 [thread overview]
Message-ID: <YxSBlPb/oZ6x0jfw@gmail.com> (raw)
In-Reply-To: <20220822114648.856734578@infradead.org>
* Peter Zijlstra <peterz@infradead.org> wrote:
> Make wait_task_inactive()'s @match_state work like ttwu()'s @state.
>
> That is, instead of an equal comparison, use it as a mask. This allows
> matching multiple block conditions.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/sched/core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3295,7 +3295,7 @@ unsigned long wait_task_inactive(struct
> * is actually now running somewhere else!
> */
> while (task_running(rq, p)) {
> - if (match_state && unlikely(READ_ONCE(p->__state) != match_state))
> + if (match_state && !(READ_ONCE(p->__state) & match_state))
> return 0;
We lose the unlikely annotation there - but I guess it probably never
really mattered anyway?
Suggestion #1:
- Shouldn't we rename task_running() to something like task_on_cpu()? The
task_running() primitive is similar to TASK_RUNNING but is not based off
any TASK_FLAGS.
Suggestion #2:
- Shouldn't we eventually standardize on task->on_cpu on UP kernels too?
They don't really matter anymore, and doing so removes #ifdefs and makes
the code easier to read.
> cpu_relax();
> }
> @@ -3310,7 +3310,7 @@ unsigned long wait_task_inactive(struct
> running = task_running(rq, p);
> queued = task_on_rq_queued(p);
> ncsw = 0;
> - if (!match_state || READ_ONCE(p->__state) == match_state)
> + if (!match_state || (READ_ONCE(p->__state) & match_state))
> ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
> task_rq_unlock(rq, p, &rf);
Suggestion #3:
- Couldn't the following users with a 0 mask:
drivers/powercap/idle_inject.c: wait_task_inactive(iit->tsk, 0);
fs/coredump.c: wait_task_inactive(ptr->task, 0);
Use ~0 instead (exposed as TASK_ANY or so) and then we can drop the
!match_state special case?
They'd do something like:
drivers/powercap/idle_inject.c: wait_task_inactive(iit->tsk, TASK_ANY);
fs/coredump.c: wait_task_inactive(ptr->task, TASK_ANY);
It's not an entirely 100% equivalent transformation though, but looks OK
at first sight: ->__state will be some nonzero mask for genuine tasks
waiting to schedule out, so any match will be functionally the same as a
0 flag telling us not to check any of the bits, right? I might be missing
something though.
Thanks,
Ingo
next prev parent reply other threads:[~2022-09-04 10:44 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-22 11:18 [PATCH v3 0/6] Freezer Rewrite Peter Zijlstra
2022-08-22 11:18 ` [PATCH v3 1/6] freezer: Have {,un}lock_system_sleep() save/restore flags Peter Zijlstra
2022-08-23 17:25 ` Rafael J. Wysocki
2022-08-22 11:18 ` [PATCH v3 2/6] freezer,umh: Clean up freezer/initrd interaction Peter Zijlstra
2022-08-23 17:28 ` Rafael J. Wysocki
2022-08-22 11:18 ` [PATCH v3 3/6] sched: Change wait_task_inactive()s match_state Peter Zijlstra
2022-09-04 10:44 ` Ingo Molnar [this message]
2022-09-06 10:54 ` Peter Zijlstra
2022-09-07 7:23 ` Ingo Molnar
2022-09-07 9:29 ` Peter Zijlstra
2022-09-07 9:30 ` Peter Zijlstra
2022-08-22 11:18 ` [PATCH v3 4/6] sched/completion: Add wait_for_completion_state() Peter Zijlstra
2022-08-23 17:32 ` Rafael J. Wysocki
2022-08-26 21:54 ` Peter Zijlstra
2022-09-04 10:46 ` Ingo Molnar
2022-09-06 10:24 ` Peter Zijlstra
2022-09-07 7:35 ` Ingo Molnar
2022-09-07 9:24 ` Peter Zijlstra
2022-08-22 11:18 ` [PATCH v3 5/6] sched/wait: Add wait_event_state() Peter Zijlstra
2022-09-04 9:54 ` Ingo Molnar
2022-09-06 11:08 ` Peter Zijlstra
2022-09-07 7:26 ` Ingo Molnar
2022-08-22 11:18 ` [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic Peter Zijlstra
2022-08-23 17:36 ` Rafael J. Wysocki
2022-09-04 10:09 ` Ingo Molnar
2022-09-06 11:23 ` Peter Zijlstra
2022-09-07 7:30 ` Ingo Molnar
2022-09-23 7:21 ` Christian Borntraeger
2022-09-23 7:53 ` Christian Borntraeger
2022-09-26 8:06 ` Christian Borntraeger
2022-09-26 10:55 ` Christian Borntraeger
2022-09-26 12:13 ` Peter Zijlstra
2022-09-26 12:32 ` Christian Borntraeger
2022-09-26 12:55 ` Peter Zijlstra
2022-09-26 13:23 ` Christian Borntraeger
2022-09-26 13:37 ` Peter Zijlstra
2022-09-26 13:54 ` Christian Borntraeger
2022-09-26 15:49 ` Christian Borntraeger
2022-09-26 18:06 ` Peter Zijlstra
2022-09-26 18:22 ` Peter Zijlstra
2022-09-27 5:35 ` Christian Borntraeger
2022-09-28 5:44 ` Christian Borntraeger
2022-10-21 17:22 ` Ville Syrjälä
2022-10-25 4:52 ` Ville Syrjälä
2022-10-25 10:49 ` Peter Zijlstra
2022-10-26 10:32 ` Ville Syrjälä
2022-10-26 11:43 ` Peter Zijlstra
2022-10-26 12:12 ` Peter Zijlstra
2022-10-26 12:14 ` Peter Zijlstra
2022-10-27 5:58 ` Chen Yu
2022-10-27 7:39 ` Peter Zijlstra
2022-10-27 13:09 ` Ville Syrjälä
2022-10-27 16:53 ` Peter Zijlstra
2022-11-02 16:57 ` Ville Syrjälä
2022-11-02 22:16 ` Peter Zijlstra
2022-11-07 11:47 ` Ville Syrjälä
2022-11-10 20:27 ` [Intel-gfx] [PATCH v3 6/6] freezer, sched: " Ville Syrjälä
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=YxSBlPb/oZ6x0jfw@gmail.com \
--to=mingo@kernel.org \
--cc=bigeasy@linutronix.de \
--cc=dietmar.eggemann@arm.com \
--cc=ebiederm@xmission.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rjw@rjwysocki.net \
--cc=rostedt@goodmis.org \
--cc=tj@kernel.org \
--cc=vincent.guittot@linaro.org \
--cc=will@kernel.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).