From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <ak@muc.de>
Subject: Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel
Date: 22 Sep 2006 14:32:15 +0200
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To: Rusty Russell <rusty@rustcorp.com.au>
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BTW I changed my copy sorry. I redid the early PDA support
to not be in assembler.

On Fri, Sep 22, 2006 at 09:59:45PM +1000, Rusty Russell wrote:
> This patch actually uses the gs register to implement the per-cpu
> sections.  It's fairly straightforward: the gs segment starts at the
> per-cpu offset for the particular cpu (or 0, in very early boot).  =

> =

> We also implement x86_64-inspired (via Jeremy Fitzhardinge) per-cpu
> accesses where a general lvalue isn't needed.  These
> single-instruction accesses are slightly more efficient, plus (being a
> single insn) are atomic wrt. preemption so we can use them to
> implement cpu_local_inc etc.

The problem is nobody uses cpu_local_inc() etc :/ And it is difficult
to use in generic code because of the usual preemption issues =

(and being slower on other archs in many cases compared to preempt disabling
around larger block of code) =


Without that it is the same code as Jeremy's variant
%gs memory reference + another reference with offset as far as I can see.

So while it looks nice I don't think it will have advantages. Or did
i miss something?

-Andi