From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Jan Kara <jack@suse.com>, Petr Mladek <pmladek@suse.com>,
Tejun Heo <tj@kernel.org>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
linux-kernel@vger.kernel.org,
Byungchul Park <byungchul.park@lge.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v10 1/2] printk: Make printk() completely async
Date: Thu, 7 Apr 2016 18:48:51 +0900 [thread overview]
Message-ID: <20160407094851.GA1349@swordfish> (raw)
In-Reply-To: <20160406082758.GA3554@quack.suse.cz>
Hello,
On (04/06/16 10:27), Jan Kara wrote:
[..]
> > Well, it's good that we have this.
> >
> > It would be better if it was runtime-controllable - changing boot
> > parameters is a bit of a pain. In fact with this approach, your
> > zillions-of-scsi-disks scenario becomes less problematic: do the async
> > offloading during the boot process then switch back to the more
> > reliable sync printing late in boot.
>
> Doing this should be relatively easy. It would be userspace's decision
> whether they want more reliable or faster printk. Sounds fine with me.
I can add it as a separate patch to the series. should be quite trivial.
I have [minor] concerns, though. I can see how, for example, user space
can decide what logging level it wants '1 4 4 7' or anything else, but
how can user space decide what printk implementation it wants to use?
I'm more or less positive not to back-port that `synchronous RW' patch
to the kernels that I use; just because I don't want to give this freedom
to people, sync printk is something I'm trying to run away from.
> > This gets normal scheduling policy, so a spinning userspace SCHED_FIFO
> > task will block printk for ever. This seems bad.
>
> I have to research this a bit but won't the SCHED_FIFO task that has
> potentially unbounded amount of work lockup the CPU even though it does
> occasional cond_resched()?
depending on `watchdog_thresh' value, it can take something like 20+
seconds before watchdog will notice softlockup.
so I'm setting printk kthread prio to `MAX_RT_PRIO - 1' as of now,
just in case.
I think I'll leave printk kthread init as a late_initcall. probably
would prefer core/arch/device init calls to happen in sync printk mode.
-ss
next prev parent reply other threads:[~2016-04-07 9:47 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-04 16:57 [PATCH v10 0/2] printk: Make printk() completely async Sergey Senozhatsky
2016-04-04 16:57 ` [PATCH v10 1/2] " Sergey Senozhatsky
2016-04-04 22:51 ` Andrew Morton
2016-04-05 5:17 ` Sergey Senozhatsky
2016-04-05 7:39 ` Sergey Senozhatsky
2016-04-06 0:19 ` Sergey Senozhatsky
2016-04-06 8:27 ` Jan Kara
2016-04-07 9:48 ` Sergey Senozhatsky [this message]
2016-04-07 12:08 ` Sergey Senozhatsky
2016-04-07 13:15 ` Jan Kara
2016-08-10 21:17 ` Viresh Kumar
2016-08-12 9:44 ` Petr Mladek
2016-08-15 14:26 ` Vladislav Levenetz
2016-08-16 9:04 ` Petr Mladek
2016-08-18 2:27 ` Sergey Senozhatsky
2016-08-18 9:33 ` Petr Mladek
2016-08-18 9:51 ` Sergey Senozhatsky
2016-08-18 10:56 ` Petr Mladek
2016-08-19 6:32 ` Sergey Senozhatsky
2016-08-19 9:54 ` Petr Mladek
2016-08-19 19:00 ` Jan Kara
2016-08-20 5:24 ` Sergey Senozhatsky
2016-08-22 4:15 ` Sergey Senozhatsky
2016-08-23 12:19 ` Petr Mladek
2016-08-24 1:33 ` Sergey Senozhatsky
2016-08-25 21:10 ` Petr Mladek
2016-08-26 1:56 ` Sergey Senozhatsky
2016-08-26 8:20 ` Sergey Senozhatsky
2016-08-30 9:29 ` Petr Mladek
2016-08-31 2:31 ` Sergey Senozhatsky
2016-08-31 9:38 ` Petr Mladek
2016-08-31 12:52 ` Sergey Senozhatsky
2016-09-01 8:58 ` Petr Mladek
2016-09-02 7:58 ` Sergey Senozhatsky
2016-09-02 15:15 ` Petr Mladek
2016-09-06 7:16 ` Sergey Senozhatsky
2016-08-23 13:03 ` Petr Mladek
2016-08-23 13:48 ` Petr Mladek
2016-04-04 16:57 ` [PATCH v10 2/2] printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky
2016-08-23 3:32 [PATCH v10 1/2] printk: Make printk() completely async Andreas Mohr
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