linux-kernel - Re: [for-next][PATCH 1/4] ring-buffer: Replace this_cpu_*() with __this_cpu

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Date:	Mon, 30 Mar 2015 07:44:30 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	stable@...r.kernel.org,
	Uwe Kleine-Koenig <u.kleine-koenig@...gutronix.de>
Subject: Re: [for-next][PATCH 1/4] ring-buffer: Replace this_cpu_*() with
 __this_cpu_*()

On Fri, 27 Mar 2015, Steven Rostedt wrote:

> Where in the patch do you see the comment? Or were you talking about
> the change log? The original patch did have a comment, an it was
> dropped, that's what I thought you were talking about.

Sorry yes the changelog.

> Actually, it is equivalent, but I do see a issue with my patch.
>
> 	val &= val & (val - 1);
>
> is the same as the more reasonable:
>
> 	val &= val - 1;
>
> I think I meant to replace &= with = :-/
>
> >
> > or more compact
> >
> > 	unsigned int val = __this_cpu_read(current_context);
> >
> > 	__this_cpu_write(current_context, val & (val - 1));
>
> Maybe I'll just use your compact version.

Hmmm... It could even be more compact

__this_cpu_and(current_context, __this_cpu_read(current_context) - 1);

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