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Date: Mon, 15 Jun 2009 14:30:55 +1000
From: Paul Mackerras <paulus@samba.org>
To: Roland Dreier <rdreier@cisco.com>
Subject: Re: [PATCH 1/2] lib: Provide generic atomic64_t implementation
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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.