linux-kernel - Re: [PATCH printk 3/5] printk: use buffer pool for sprint buffers

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Message-ID: <20200930093552.3684aee1@gandalf.local.home>
Date:   Wed, 30 Sep 2020 09:35:52 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Petr Mladek <pmladek@...e.com>,
        John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk 3/5] printk: use buffer pool for sprint buffers

On Wed, 30 Sep 2020 10:06:24 +0200
Rasmus Villemoes <rasmus.villemoes@...vas.dk> wrote:

> True. But remember that printk is called from _everywhere_, with all
> sorts of locks held and/or preemption disabled or whatnot, and every
> cycle spent in printk makes those windows wider. Doubling the cost of
> every single printk by unconditionally doing vsnprintf() twice is a bad
> idea.

But the console output is usually magnitudes more expensive than the
vsnprintf(), would doing it twice really make a difference?

-- Steve