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

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Date:	Tue, 27 Aug 2013 15:37:16 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
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 Tue, 27 Aug 2013, Geert Uytterhoeven wrote:

> 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 ;-)

Ok fixed that as well.

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