linux-kernel - Re: [PATCH] percpu: add optimized generic percpu accessors

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Date:	Fri, 16 Jan 2009 09:10:15 -0500
From:	Mark Lord <lkml@....ca>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	ebiederm@...ssion.com, cl@...ux-foundation.org,
	rusty@...tcorp.com.au, travis@....com,
	linux-kernel@...r.kernel.org, steiner@....com, hugh@...itas.com
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors

Andrew Morton wrote:
> On Thu, 15 Jan 2009 19:02:59 +0100 Ingo Molnar <mingo@...e.hu> wrote:
> 
>> * Andrew Morton <akpm@...ux-foundation.org> wrote:
..
>>> I wonder if the preempt_disable()/preempt_enable() in here actually
>>> does anything useful on any architecture.
>> Provides "this is IRQ safe"
> 
> ?
> 
>> and "this is preempt safe" semantics.
> 
> Of course.  But do any architectures actually _need_ that for a single read?
..

If the target is unaligned, then RISC architectures will need protection there.
If we can guarantee correct memory alignment of the target, then no / none.

Cheers
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