Message-ID: <526EC31D.4070802@vmware.com>
Date: Mon, 28 Oct 2013 22:03:41 +0200
From: Heikki Linnakangas <hlinnakangas@vmware.com>
Organization: VMware
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To: Andres Freund <andres@2ndquadrant.com>
CC: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>,
 Peter Geoghegan <pg@heroku.com>,
 Pg Hackers <pgsql-hackers@postgresql.org>, Ants Aasma <ants@cybertec.at>
Subject: Re: better atomics
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On 28.10.2013 21:32, Andres Freund wrote:
> On 2013-10-28 15:02:41 -0400, Robert Haas wrote:
>> Most of the academic papers I've read on
>> implementing lock-free or highly-parallel constructs attempt to
>> confine themselves to 8-byte operations with 8-byte compare-and-swap,
>> and I'm a bit disposed to think we ought to try to hew to that as
>> well.  I'm not dead set against going further, but I lean against it,
>> for all of the reasons mentioned above.
>
> I think there are quite some algorithms relying on 16byte CAS, that's
> why I was thinking about it at all. I think it's easier to add support
> for it in the easier trawl through the compilers, but I won't argue much
> for it otherwise for now.

Many algorithms require a 2*(pointer width) CAS instruction. On 64-bit 
platforms that's 16 bytes, but on 32-bit platforms an 8 byte version 
will suffice.

- Heikki


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