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

From	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async
Date	2016-03-07 13:40 +0100
Message-ID	<ra2C5-2QS-1@gated-at.bofh.it> (permalink)
References	<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> <ra2iK-2IY-11@gated-at.bofh.it>
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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.
> > 
> > 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.
> > 
> > So if this will be a problem in practice, using a kthread will probably be
> > the easiest solution.
> 
> Hum, and thinking more about it: Considering that WQ_MEM_RECLAIM workqueues
> create kthread anyway as a rescuer thread, it may be the simplest to just
> go back to using a single kthread for printing. What do you think?
> 

I think a plain kthread is better. printing_work_func() can become a buggy
function. console_unlock() from printing_work_func() can occupy kworker for
many seconds due to looping with cond_resched() (i.e. without calling
schedule_timeout_*()) from schedulable context which can in turn defer
other work items.

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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