linux-kernel - Re: [RFC][PATCHv4 0/7] printk: introduce printing kernel threads

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Date:   Fri, 30 Jun 2017 21:45:16 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Andreas Mohr <andi@...as.de>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCHv4 0/7] printk: introduce printing kernel threads

On (06/30/17 14:11), Petr Mladek wrote:
> > 2) can offload printing to other CPUs from vprintk_emit()
> >    and avoid any of scheduler->timekeeping->etc. paths. which will
> >    replace printk_deferred().
> 
> I probably miss something. There is still called wake_up_process()
> in this patchset and we could not do this in some scheduler and
> timekeeping paths. Also we must not take the console_lock() in
> these paths because it calls wake_up_process() as well. But
> we want to flush few lines when possible.

yes. but we could call wake_up_process() on !this_cpu.
so we wouldn't take this_cpu ->rq lock and so on.

	CPU1

	vprintk_emit()
		wake_up_process(printk_kthread on CPU2);

	-ss