linux-kernel - Re: [PATCH 1/2] lib: Provide generic atomic64

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Message-ID: <18997.52863.576426.501025@cargo.ozlabs.ibm.com>
Date:	Mon, 15 Jun 2009 14:30:55 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Avi Kivity <avi@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	benh@...nel.crashing.org, akpm@...ux-foundation.org,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lib: Provide generic atomic64_t implementation

Roland Dreier writes:

> FWIW, Nehalem EX actually goes to 8 cores/16 threads per socket.  But
> worrying about 32-bit performance on Nehalem is a little silly -- this
> simplest solution is simply to run a 64-bit kernel.

I'm not worried about ANY x86 processor, 32-bit or 64-bit, in fact,
since x86 already has an atomic64_t implementation for both 32-bit and
64-bit.

It is interesting, though, that arch/x86/include/asm/atomic_32.h
unconditionally uses cmpxchg8b to implement atomic64_t, but I thought
that cmpxchg8b didn't exist in processors prior to the Pentium.
Presumably you can't use perf_counters on a 386 or 486.

Paul.
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