From: Valentin Schneider <valentin.schneider@arm.com>
To: Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Julien Thierry <julien.thierry@arm.com>
Subject: preempt_schedule_irq() loop question
Date: Wed, 16 Jan 2019 12:50:42 +0000 [thread overview]
Message-ID: <cc989920-a13b-d53b-db83-1584a7f53edc@arm.com> (raw)
Hi,
I've been wandering around preempt_schedule_irq() in sched/core.c, and
got curious regarding how the arch code calls it.
The main part of preempt_schedule_irq() is:
do {
preempt_disable();
local_irq_enable();
__schedule(true);
local_irq_disable();
sched_preempt_enable_no_resched();
} while (need_resched());
Yet all the arch entry.S I looked at (I stopped after arm64, arm, x86_32,
MIPS, powerpc) wrap the call to preempt_schedule_irq() in another
do { ... } while (need_resched())
For instance, this is what's done in arm64:
1: bl preempt_schedule_irq // irq en/disable is done inside
ldr x0, [tsk, #TSK_TI_FLAGS] // get new tasks TI_FLAGS
tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling?
I naively thought this could be attributed to something like
preempt_schedule_irq() historically not having an inner loop, but it seems
to have been there since the beginning of time (or at least up to the point
where the git history stops).
I don't see why we need to have these nested loops - AFAICT the one in
preempt_schedule_irq() would suffice. What am I missing?
next reply other threads:[~2019-01-16 12:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-16 12:50 Valentin Schneider [this message]
2019-01-16 13:45 ` preempt_schedule_irq() loop question Peter Zijlstra
2019-01-16 14:57 ` Thomas Gleixner
2019-01-16 15:23 ` Valentin Schneider
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=cc989920-a13b-d53b-db83-1584a7f53edc@arm.com \
--to=valentin.schneider@arm.com \
--cc=catalin.marinas@arm.com \
--cc=julien.thierry@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=will.deacon@arm.com \
/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).