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Date: Wed, 7 Nov 2018 12:45:20 +0100
From: Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH v6 1/3] printk: Add line-buffered printk() API.
Message-ID: <20181107114520.bi3ur2fpn62rlyje@pathway.suse.cz>
References: <1541165517-3557-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
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To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Dmitriy Vyukov <dvyukov@google.com>, Steven Rostedt <rostedt@goodmis.org>, Alexander Potapenko <glider@google.com>, Fengguang Wu <fengguang.wu@intel.com>, Josh Poimboeuf <jpoimboe@redhat.com>, LKML <linux-kernel@vger.kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Will Deacon <will.deacon@arm.com>

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