linux-kernel - Re: [PATCH v6 1/3] printk: Add line-buffered printk() API.

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Message-ID: <20181107114520.bi3ur2fpn62rlyje@pathway.suse.cz>
Date:   Wed, 7 Nov 2018 12:45:20 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v6 1/3] printk: Add line-buffered printk() API.

On Wed 2018-11-07 19:52:53, Tetsuo Handa wrote:
> On 2018/11/06 23:35, Sergey Senozhatsky wrote:
> > - Do not allocate seq_buf if we are in printk-safe or in printk-nmi mode.
> >   To avoid "buffering for the sake of buffering". IOW, when in printk-safe
> >   use printk-safe.
> 
> Why? Since printk_safe_flush_buffer() forcibly flushes the partial line,
> calling printk_safe_log_store() after line buffering can reduce possibility of
> flushing partial lines, can't it?

Good point.

Well, printk_safe buffers are flushed via irqwork scheduled on the
same CPU. It might get flushed prematurely from other CPU but
I am not sure if this risk is worth the double buffering.

Best Regards,
Petr