linux-kernel - Re: [PATCH] NMI: fix NMI period is not correct when cpu frequency changes issue.

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Message-Id: <20130415212914.936f903a.akpm@linux-foundation.org>
Date:	Mon, 15 Apr 2013 21:29:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Pan, Zhenjie" <zhenjie.pan@...el.com>
Cc:	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"acme@...stprotocols.net" <acme@...stprotocols.net>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Liu, Chuansheng" <chuansheng.liu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NMI: fix NMI period is not correct when cpu frequency
 changes issue.

On Tue, 16 Apr 2013 03:45:15 +0000 "Pan, Zhenjie" <zhenjie.pan@...el.com> wrote:

> > Overall the patch looks desirable, but it increases the kernel size by several
> > hundred bytes when CONFIG_CPU_FREQ=n.  It should produce no code in
> > this case!  Take a look at the magic in register_hotcpu_notifier(), the way in
> > which it causes all the code to be removed by the compiler in the
> > CONFIG_HOTPLUG_CPU=n case.  That trick can be used here.
> 
> I have checked if CONFIG_CPU_FREQ=n, cpufreq_register_notifier() will be a blank function.
> So I think it will not increases the kernel size.

I tested it.  The patch adds ~350 bytes of dead code.

This is partly an infrastructural problem: unlike
register_hotcpu_notifier(), the cpufreq notifier code lacks the
infrastructure with which we can prevent this problem.

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