From: "Jörn Engel" <joern@purestorage.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>
Subject: Re: sched: wakeup setting TIF_NEED_RESCHED too frequently
Date: Wed, 28 Apr 2021 11:51:24 -0700 [thread overview]
Message-ID: <YImurOENWBEg8UP+@cork> (raw)
In-Reply-To: <YIkdDeb9c+XmDRvM@hirez.programming.kicks-ass.net>
On Wed, Apr 28, 2021 at 10:30:05AM +0200, Peter Zijlstra wrote:
>
> set_nr_if_polling() only sets TIF_NEED_RESCHED IFF TIF_POLLING_NRFLAG is
> set. TIF_POLLING_NRFLAG is only set when idle and is then sufficient to
> wake that cpu and reschedule.
>
> If not TIF_POLLING_NRFLAG, then we send an IPI to deal with the
> non-empty wake_list.
Yeah, saw that myself. My explanation of the behaviour is wrong. The
observed behaviour remains, though.
Guess I have to add more instrumentation if I cannot find the cause by
reading the code.
Thank you!
Jörn
--
Optimizations always bust things, because all optimizations are, in
the long haul, a form of cheating, and cheaters eventually get caught.
-- Larry Wall
prev parent reply other threads:[~2021-04-28 18:52 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 21:16 sched: wakeup setting TIF_NEED_RESCHED too frequently Jörn Engel
2021-04-28 8:30 ` Peter Zijlstra
2021-04-28 18:51 ` Jörn Engel [this message]
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