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

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Date:   Wed, 30 Sep 2020 14:32:12 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Steven Rostedt' <rostedt@...dmis.org>,
        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" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH printk 3/5] printk: use buffer pool for sprint buffers

From: Steven Rostedt
> Sent: 30 September 2020 14:36
> 
> 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?

Are there any strange %pX modifiers that do anything really horrid?

	David

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