From: Thomas Gleixner <tglx@linutronix.de>
To: Song Chen <chensong_2000@189.cn>
Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
rostedt@goodmis.org, mingo@redhat.com, peterz@infradead.org,
juri.lelli@redhat.com, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, keescook@chromium.org,
gregkh@linuxfoundation.org, maz@kernel.org, joe@perches.com,
romain.perier@gmail.com, john.garry@huawei.com
Subject: Re: [PATCH] kernel:irq:manage: request threaded irq with a specified priority
Date: Tue, 13 Apr 2021 10:39:39 +0200 [thread overview]
Message-ID: <875z0qzigk.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <1618294774-24370-1-git-send-email-chensong_2000@189.cn>
On Tue, Apr 13 2021 at 14:19, Song Chen wrote:
> In general, irq handler thread will be assigned a default priority which
> is MAX_RT_PRIO/2, as a result, no one can preempt others.
>
> Here is the case I found in a real project, an interrupt int_a is
> coming, wakes up its handler handler_a and handler_a wakes up a
> userspace RT process task_a.
>
> However, if another irq handler handler_b which has nothing to do
> with any RT tasks is running when int_a is coming, handler_a can't
> preempt handler_b, as a result, task_a can't be waken up immediately
> as expected until handler_b gives up cpu voluntarily. In this case,
> determinism breaks.
It breaks because the system designer failed to assign proper priorities
to the irq threads int_a, int_b and to the user space process task_a.
That's not solvable at the kernel level.
Thanks,
tglx
next prev parent reply other threads:[~2021-04-13 8:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 6:19 [PATCH] kernel:irq:manage: request threaded irq with a specified priority Song Chen
2021-04-13 8:39 ` Thomas Gleixner [this message]
2021-04-16 4:57 ` chensong
2021-04-16 7:15 ` Daniel Bristot de Oliveira
2021-04-16 9:09 ` Thomas Gleixner
2021-04-18 14:33 ` chensong
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=875z0qzigk.ffs@nanos.tec.linutronix.de \
--to=tglx@linutronix.de \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=chensong_2000@189.cn \
--cc=dietmar.eggemann@arm.com \
--cc=gregkh@linuxfoundation.org \
--cc=joe@perches.com \
--cc=john.garry@huawei.com \
--cc=juri.lelli@redhat.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=maz@kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=romain.perier@gmail.com \
--cc=rostedt@goodmis.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 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).