linux-kernel - Re: [GIT PULL v2] printk: Make it usable on nohz cpus

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Message-ID: <20121208150252.GI12011@gmail.com>
Date:	Sat, 8 Dec 2012 16:02:52 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Anish Kumar <anish198519851985@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [GIT PULL v2] printk: Make it usable on nohz cpus

* Frederic Weisbecker <fweisbec@...il.com> wrote:

> Ingo,
> 
> Please pull the printk support in dynticks mode patches that can
> be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git tags/printk-dynticks-for-mingo-v2
> 
> for you to fetch changes up to 74876a98a87a115254b3a66a14b27320b7f0acaa:
> 
>   printk: Wake up klogd using irq_work (2012-11-18 01:01:49 +0100)
> 
> It is based on v3.7-rc4.
> 
> Changes since previous pull request include support for irq 
> work flush on CPU offlining and acks from Steve. The rest 
> hasn't changed except some comment fix.

Since this changes kernel/printk.c it needs Linus's ack.

I looked through the older submissions but found no good summary 
of these changes: it would be nice if you could write up a good 
high level description of these changes - why has printk based 
kernel message logging become problematic on nohz, what are the 
symptoms to users, and what are the solution alternatives you 
found and please justify the irq_work extension variant you 
picked.

I more or less accept the fact that fixes are needed here, but 
the linecount appears a bit high. It's possibly unavoidable, but 
would be nice to have a discussion of it, as printk is something 
we really, really want to keep as simple as possible.

Thanks,

	Ingo
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