linux-kernel - Re: [RFD 1/9] Change cpustat fields to an array.

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Message-ID: <1317223416.24040.49.camel@twins>
Date:	Wed, 28 Sep 2011 17:23:36 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, paul@...lmenage.org,
	lizf@...fujitsu.com, daniel.lezcano@...e.fr,
	jbottomley@...allels.com
Subject: Re: [RFD 1/9] Change cpustat fields to an array.

On Wed, 2011-09-28 at 12:13 -0300, Glauber Costa wrote:
> On 09/27/2011 06:00 PM, Peter Zijlstra wrote:
> > On Fri, 2011-09-23 at 19:20 -0300, Glauber Costa wrote:
> >>   /* Must have preemption disabled for this to be meaningful. */
> >> -#define kstat_this_cpu __get_cpu_var(kstat)
> >> +#define kstat_this_cpu this_cpu_ptr(task_group_kstat(current))
> >
> > This just lost you a debug check, the former would whinge when called
> > without preemption, the new one wont. Its part of the this_cpu feature
> > set to make debugging impossible.
> 
> Why is that?
> 
> from percpu.h:
> #define __get_cpu_var(var) (*this_cpu_ptr(&(var)))
> 
> So I don't get it.

Ah, my bad, its not actually part of the this_cpu*() api, what wonderful
mess that is.
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