From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Luo Jiaxing <luojiaxing@huawei.com>,
sergey.senozhatsky@gmail.com, rostedt@goodmis.org,
john.ogness@linutronix.de, linux-kernel@vger.kernel.org,
linuxarm@huawei.com, bobo.shaobowang@huawei.com
Subject: Re: [PATCH] printk: stop spining waiter when console resume to flush prb
Date: Mon, 10 May 2021 17:26:45 +0900 [thread overview]
Message-ID: <YJjuRV57eO3Pp/bp@google.com> (raw)
In-Reply-To: <YJVsgPc66lhaAUN0@alley>
On (21/05/07 18:36), Petr Mladek wrote:
> > console_unlock()
> > {
> > ...
> >
> > if (printed_messages > limit && !console_lock_spinning_disable_and_check()) {
> > printk_safe_exit_irqrestore(flags);
> >
> > console_locked = 0;
> > up_console_sem();
> >
> > defer_console_output();
> > return;
> > }
> >
> > ...
> > }
>
> No, please, no.
>
Well, the alternative patch set just gives everyone an API that selectively
downgrades printk() to pre-console_sem_owner age: when console_unlock()
would never handover the printing duty. It'll take no time until this
function will pop up somewhere where we don't want it to be used.
E.g.
rcu_read_lock();
...
console_unlock_preemptible();
...
rcu_read_unlock();
lockdep_assert_preemption_enabled() is not entirely reliable - it
depends on __lockdep_enabled, provided that system in question has
CONFIG_PROVE_LOCKING set.
> Not to say, that defer_console_output() would trigger IRQ on the same
> CPU again and again.
You mean only on archs that have arch_irq_work_raise()?
It queues the work IF we have pending messages AND there are NO active
console_sem waiters spinning on consolse_sem waiting for us to handover
the printing duty. And IRQ shall write to consoles only N messages out
of possibly M pending messages (M > N). N, obviously, should be small,
e.g. 42 lines: if after 42 printed lines we didn't handover printing
to another context then - queue another IRQ work and iret. But it keeps
the console_owner mechanism enabled.
next prev parent reply other threads:[~2021-05-10 8:26 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 8:00 [PATCH] printk: stop spining waiter when console resume to flush prb Luo Jiaxing
2021-05-06 13:13 ` Steven Rostedt
2021-05-07 8:35 ` luojiaxing
2021-05-06 13:39 ` Petr Mladek
2021-05-06 14:07 ` Sergey Senozhatsky
2021-05-06 14:12 ` Sergey Senozhatsky
2021-05-06 15:14 ` John Ogness
2021-05-07 7:58 ` luojiaxing
2021-05-07 7:33 ` luojiaxing
2021-05-07 7:49 ` Sergey Senozhatsky
2021-05-07 16:36 ` Petr Mladek
2021-05-10 8:26 ` Sergey Senozhatsky [this message]
2021-05-10 10:17 ` Petr Mladek
2021-05-10 10:32 ` John Ogness
2021-05-10 11:16 ` Sergey Senozhatsky
2021-05-10 11:43 ` Sergey Senozhatsky
2021-05-07 16:13 ` Petr Mladek
2021-05-10 8:29 ` luojiaxing
2021-05-10 9:50 ` Petr Mladek
2021-05-10 12:06 ` Sergey Senozhatsky
2021-05-10 7:41 ` luojiaxing
2021-05-10 9:30 ` Petr Mladek
2021-05-11 7:32 ` luojiaxing
2021-05-11 9:08 ` Petr Mladek
2021-05-13 7:55 ` luojiaxing
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=YJjuRV57eO3Pp/bp@google.com \
--to=senozhatsky@chromium.org \
--cc=bobo.shaobowang@huawei.com \
--cc=john.ogness@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxarm@huawei.com \
--cc=luojiaxing@huawei.com \
--cc=pmladek@suse.com \
--cc=rostedt@goodmis.org \
--cc=sergey.senozhatsky@gmail.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).