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From: James Cloos <cloos@jhcloos.com>
To: Graeme B. Bell <graeme.bell@nibio.no>
Cc: Andres Freund <andres@anarazel.de>
Cc: Merlin Moncure <mmoncure@gmail.com>
Cc: Craig James <cjames@emolecules.com>
Cc: Joshua D. Drake <jd@commandprompt.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Hmmm... why does CPU-intensive pl/pgsql code parallelise so badly when queries parallelise fine? Anyone else seen this?
Date: Sat, 11 Jul 2015 19:18:21 -0400
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>>>>> "GBB" == Graeme B Bell <graeme.bell@nibio.no> writes:

GBB> 1a. For example AMD CPUs list the number of integer cores (e.g. 16),
GBB> but there is actually only half as many cores available for floating
GBB> point work (8). So if your functions need to use floating point, your
GBB> scaling will suffer badly on FP functions.

That is half as many 256-bit float units; for scalar math and for
128-bit vector math each core gets a half of the float unit.

Only for the 256-bit vector math do the schedulars have to compete for
float unit access.

-JimC
-- 
James Cloos <cloos@jhcloos.com>         OpenPGP: 0x997A9F17ED7DAEA6


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  Subject: Re: Hmmm... why does CPU-intensive pl/pgsql code parallelise so badly when queries parallelise fine? Anyone else seen this?
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