linux-kernel - Re: [guv v2 20/31] powerpc: Replace __get_cpu

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Date:	Tue, 27 Aug 2013 10:44:06 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [guv v2 20/31] powerpc: Replace __get_cpu_var uses

On Mon, Aug 26, 2013 at 10:44 PM, Christoph Lameter <cl@...ux.com> wrote:
> __get_cpu_var() is used for multiple purposes in the kernel source. One of them is
> address calculation via the form &__get_cpu_var(x). This calculates the address for
> the instance of the percpu variable of the current processor based on an offset.
>
> Others usage cases are for storing and retrieving data from the current processors percpu area.

use cases

> __get_cpu_var() always only does a address determination. However, store and retrieve operations

an address

> This patch converts __get_cpu_var into either and explicit address calculation using this_cpu_ptr()

an explicit

> 4. Retrieve the content of a percpu struct
>
>         DEFINE_PER_CPU(struct mystruct, y);
>         struct mystruct x = __get_cpu_var(y);
>
>    Converts to
>
>         memcpy(this_cpu_ptr(&y), x, sizeof(x));

Let's hope the actual code copies in the other direction ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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