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Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async

From Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async
Date 2016-03-07 15:50 +0100
Message-ID <ra4DU-46c-5@gated-at.bofh.it> (permalink)
References (5 earlier) <r9EJr-4dl-1@gated-at.bofh.it> <r9GUW-5zH-5@gated-at.bofh.it> <r9YI9-oh-5@gated-at.bofh.it> <ra0qC-1wR-25@gated-at.bofh.it> <ra13k-1LB-13@gated-at.bofh.it>
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On (03/07/16 11:52), Jan Kara wrote:
[..]
> So for UP systems, we should by default disable async printing anyway I
> suppose. It is just a pointless overhead. So please just make printk_sync
> default to true if !CONFIG_SMP.

ok, thanks.

> When IRQs are disabled, you're right we will have a change in behavior. I
> don't see an easy way of avoiding delaying of printk until IRQs get
> enabled. I don't want to queue work directly because that creates
> possibility for lock recursion in queue_work(). And playing some tricks
> with irq_works isn't easy either - you cannot actually rely on any other
> CPU doing anything (even a timer tick) because of NOHZ.

yes. I thought about some sort of PRINTK_IPI on smp, and queue work from
PRINTK_IPI. which is a bit insane.

> So if this will be a problem in practice, using a kthread will probably be
> the easiest solution.

probably kthread is the way to go then. Tetsuo's bad experience with
workqueues also sounds a bit alarming.

I'll post a new patch soon.

	-ss

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Thread

[RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-05 12:00 +0100
  Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-06 07:40 +0100
    Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-03-06 08:20 +0100
      Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-06 10:40 +0100
        Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-03-06 12:10 +0100
          Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-06 14:30 +0100
            Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-03-06 16:00 +0100
            Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-07 09:30 +0100
              Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-07 11:20 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-07 12:00 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-07 13:20 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-03-07 13:40 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-07 16:20 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tejun Heo <tj@kernel.org> - 2016-03-07 17:00 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-08 11:30 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tejun Heo <tj@kernel.org> - 2016-03-11 18:30 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-12 06:10 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-09 07:10 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-10 10:30 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-10 17:00 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Petr Mladek <pmladek@suse.com> - 2016-03-10 11:00 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-10 17:30 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-07 15:50 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-03-07 12:20 +0100
                Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-07 15:40 +0100
              Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async Tejun Heo <tj@kernel.org> - 2016-03-07 16:50 +0100

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