Date: Tue, 29 Jun 1999 12:17:08 -0700 From: Erich Boleyn <erich@uruk.org> To: Kevin Van Maren <vanmaren@fast.cs.utah.edu> Cc: freebsd-smp@FreeBSD.ORG Subject: Re: high-efficiency SMP locks - submission for review Message-ID: <E10z3NU-0002Gf-00@uruk.org> In-Reply-To: Your message of "Tue, 29 Jun 1999 13:08:28 MDT." <199906291908.NAA08028@fast.cs.utah.edu>
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Kevin Van Maren <vanmaren@fast.cs.utah.edu> wrote:
> [from Richard Cownie]:
> > No, you can have a non-aligned locked access - there's a bunch of
> > complex and ugly stuff ("split locks", the SPLCK# bus signal) in
> > the P6 bus protocol to support this. But don't do it if you can
> > possibly avoid it - it's inefficient, and since it exercises arcane
> > features of the hardware, it could be buggy.
>
> My understanding is that it is only guaranteed to be atomic for the
> processor family if it is naturally-aligned, although current
> processors ALSO provide atomic operatings for unaligned accesses.
> My point is that we should not rely on unaligned accesses being
> atomic, as per intel documentation.
It is guaranteed, and is in the Intel documentation.
But as mentioned, you would really prefer locking on aligned addresses... ;)
--
Erich Stefan Boleyn \_ <erich@uruk.org>
Mad but Happy Scientist \__ http://www.uruk.org/
Motto: "I'll live forever or die trying" ---------------------------
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