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Date: Tue, 21 Aug 2007 23:12:00 +0200
From: Maciej Sobczak <prog@msobczak.com>
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To: John Baldwin <jhb@freebsd.org>
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Cc: freebsd-arch@FreeBSD.org
Subject: Re: Lockless uidinfo.
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John Baldwin wrote:

> Memory barriers on another CPU don't mean anything about the CPU thread 2 is 
> on.

Of course they do. Otherwise they would be completely useless.

 > Memory barriers do not flush caches on other CPUs, etc.

Membars are not about caches, but about visibility and ordering. Cache 
is transparent and that is guaranteed by hardware - there is no need to 
involve any software tricks to make cache work correctly. You can 
influence their performance, but not correctness.

-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/