linux-kernel - Re: [this_cpu_xx V4 00/20] Introduce per cpu atomic operations and avoid per cpu address arithmetic

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Message-ID: <20091002173246.GB4884@elte.hu>
Date:	Fri, 2 Oct 2009 19:32:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au,
	Pekka Enberg <penberg@...helsinki.fi>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [this_cpu_xx V4 00/20] Introduce per cpu atomic operations and
	avoid per cpu address arithmetic


* Christoph Lameter <cl@...ux-foundation.org> wrote:

> On Fri, 2 Oct 2009, Ingo Molnar wrote:
> 
> > One final step/cleanup seems to be missing from it: it should 
> > replace current uses of percpu_op() [percpu_read(), etc.] in the x86 
> > tree and elsewhere with the new this_cpu_*() primitives. 
> > this_cpu_*() is using per_cpu_from_op/per_cpu_to_op directly, we 
> > dont need those percpu_op() variants anymore.
> 
> Well after things settle with this_cpu_xx we can drop those.
> 
> > There should also be a kernel image size comparison done for that 
> > step, to make sure all the new primitives are optimized to the max 
> > on the instruction level.
> 
> Right. There will be a time period in which other arches will need to 
> add support for this_cpu_xx first.

Size comparison should be only on architectures that support it (i.e. 
x86 right now). The generic fallbacks might be bloaty, no argument about 
that. ( => the more reason for any architecture to add optimizations for 
this_cpu_*() APIs. )

	Ingo
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