From: | andres(at)anarazel(dot)de (Andres Freund) |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Ants Aasma <ants(at)cybertec(dot)at> |
Subject: | Re: better atomics - v0.6 |
Date: | 2014-09-24 16:57:56 |
Message-ID: | 20140924165756.GS2521@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-09-24 12:44:09 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On 2014-09-24 18:55:51 +0300, Heikki Linnakangas wrote:
> >> There doesn't seem to be any hardware implementations of that in the patch.
> >> Is there any architecture that has an instruction or compiler intrinsic for
> >> that?
>
> > You can implement it rather efficiently on ll/sc architectures. But I
> > don't really think it matters. I prefer add_until (I've seen it named
> > saturated add before as well) to live in the atomics code, rather than
> > reimplement it in atomics employing code. I guess you see that
> > differently?
>
> I think the question is more like "what in the world happened to confining
> ourselves to a small set of atomics".
I fail to see why the existance of a wrapper around compare-exchange
(which is one of the primitives we'd agreed upon) runs counter to
the agreement that we'll only rely on a limited number of atomics on the
hardware level?
> I doubt either that this exists
> natively anywhere, or ethat it's so useful that we should expect platforms
> to have efficient implementations.
It's useful for my work to get rid of most LockBufHdr() calls (to
manipulate usagecount locklessly). That's why I added it. We can delay
it till that patch is ready, but I don't really see the benefit.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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