From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anna-Maria Behnsen <anna-maria@linutronix.de>,
Marcelo Tosatti <mtosatti@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Peter Xu <peterx@redhat.com>,
Nitesh Narayan Lal <nitesh@redhat.com>,
Alex Belits <abelits@marvell.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
John Stultz <john.stultz@linaro.org>
Subject: Re: [patch 7/8] hrtimer: Avoid unnecessary SMP function calls in clock_was_set()
Date: Sat, 15 May 2021 01:28:39 +0200 [thread overview]
Message-ID: <YJ8Hp0gTGwugxxFM@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <87bl9d407i.ffs@nanos.tec.linutronix.de>
On Fri, May 14, 2021 at 08:52:33PM +0200, Thomas Gleixner wrote:
> On Thu, May 13 2021 at 16:59, Peter Zijlstra wrote:
> > On Tue, Apr 27, 2021 at 10:25:44AM +0200, Thomas Gleixner wrote:
> >> - /* Retrigger the CPU local events everywhere */
> >> - on_each_cpu(retrigger_next_event, NULL, 1);
> >> + if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
> >> + on_each_cpu(retrigger_next_event, NULL, 1);
> >
> > This will violate NOHZ_FULL;
>
> Only if that allocation fails.
Right, which should be near to never I suppose.
> Aside of that any CPU which has an affected timer will get notified even
> on NOHZ_FULL.
Right; but if it's properly NOHZ_FULL -- the kind that wanted a signal
on any entry into the kernel -- when it won't have timers and this IPI
will trigger the signal and kill the program.
But yeah, you're right, that's not very likely.
> >> + preempt_disable();
> >> + smp_call_function_many(mask, retrigger_next_event, NULL, 1);
> >
> > The sane option is:
> >
> > smp_call_function_many_cond(cpu_online_mask, retrigger_next_event,
> > NULL, SCF_WAIT, update_needs_ipi);
> >
> > Which does all of the above, but better.
>
> With the difference that the for_each_cpu() loop runs with preemption
> disabled, while with this approach preemption is only disabled accross
> the function call.
Yeah, I'd forgotten that... I might put looking at that on the todo list
somewhere :/
next prev parent reply other threads:[~2021-05-14 23:29 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 8:25 [patch 0/8] hrtimers: Overhaul the clock_was_set() logic Thomas Gleixner
2021-04-27 8:25 ` [patch 1/8] hrtimer: Ensure timerfd notification for HIGHRES=n Thomas Gleixner
2021-04-27 8:25 ` [patch 2/8] hrtimer: Force clock_was_set() handling for the HIGHRES=n, NOHZ=y case Thomas Gleixner
2021-05-12 14:59 ` Peter Zijlstra
2021-05-12 16:40 ` Thomas Gleixner
2021-04-27 8:25 ` [patch 3/8] timerfd: Provide timerfd_resume() Thomas Gleixner
2021-04-27 8:25 ` [patch 4/8] timekeeping: Distangle resume and clock-was-set events Thomas Gleixner
2021-04-27 8:25 ` [patch 5/8] time/timekeeping: Avoid invoking clock_was_set() twice Thomas Gleixner
2021-04-27 8:25 ` [patch 6/8] hrtimer: Add bases argument to clock_was_set() Thomas Gleixner
2021-04-27 8:25 ` [patch 7/8] hrtimer: Avoid unnecessary SMP function calls in clock_was_set() Thomas Gleixner
2021-05-13 14:59 ` Peter Zijlstra
2021-05-14 18:52 ` Thomas Gleixner
2021-05-14 23:28 ` Peter Zijlstra [this message]
2021-05-15 0:24 ` Thomas Gleixner
2021-04-27 8:25 ` [patch 8/8] hrtimer: Avoid more " Thomas Gleixner
2021-04-27 15:11 ` Marcelo Tosatti
2021-04-27 19:59 ` Thomas Gleixner
2021-04-30 7:12 ` [patch V2 " Thomas Gleixner
2021-04-30 16:49 ` Marcelo Tosatti
2021-05-13 7:47 ` Peter Zijlstra
2021-05-14 19:08 ` Thomas Gleixner
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=YJ8Hp0gTGwugxxFM@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=abelits@marvell.com \
--cc=anna-maria@linutronix.de \
--cc=frederic@kernel.org \
--cc=john.stultz@linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mtosatti@redhat.com \
--cc=nitesh@redhat.com \
--cc=peterx@redhat.com \
--cc=rjw@rjwysocki.net \
--cc=tglx@linutronix.de \
/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).