Re: SSE2

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: SSE2
Date	2012-07-31 14:29 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2012Jul31.162943@mips.complang.tuwien.ac.at> (permalink)
References	<2012Jul27.165605@mips.complang.tuwien.ac.at> <81078807968435@frunobulax.edu>

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mhx@iae.nl (Marcel Hendrix) writes:
>anton@mips.complang.tuwien.ac.at (Anton Ertl) writes Re: SSE2
>> My _guess_ is that your compiler produces some stack memory stores for
>> some of the variants, with some stack memory fetches soon after, and
>> these cost quie a bit of performance.  At least they used to.
>
>I would be interested to read more about this. What is the problem here,
>exactly? Is a stackframe better than push/pop?

At least in earlier CPUs a dependency through memory had a long
latency, like 15 cycles or so (and all stuff that went through memory
was affected): the data went in the store buffer and eventually went
out to cache, and only then the load could access it for real.  I
think newer CPUs have added a bypass (store-to-load-forwarding) to
make such cases faster; or maybe they just made the case faster where
the address of the store is different from the address of the load
(i.e., no bypass).

A benchmark I used was a simple counted loop where the counter was in
memory.  IIRC this needed about 15 cycles/iteration or so on Athlon
and Pentium 3.

Forth systems that are not very sophisticated (or for sophisticated
compilers, a fallback option) might storing stack items to the
stack-in memory and soon after load that iterm from the stack, and
so might run into this problem.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
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SSE2 mhx@iae.nl (Marcel Hendrix) - 2012-07-27 16:20 +0200
  Re: SSE2 Paul Rubin <no.email@nospam.invalid> - 2012-07-27 08:03 -0700
    Re: SSE2 mhx@iae.nl (Marcel Hendrix) - 2012-07-28 15:28 +0200
  Re: SSE2 anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-27 14:56 +0000
    Re: SSE2 Paul Rubin <no.email@nospam.invalid> - 2012-07-27 08:56 -0700
      Re: SSE2 anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-27 16:28 +0000
      Re: SSE2 David Kuehling <dvdkhlng@gmx.de> - 2012-07-28 01:47 +0200
        Re: SSE2 mhx@iae.nl (Marcel Hendrix) - 2012-07-31 00:28 +0200
          Re: SSE2 David Kuehling <dvdkhlng@gmx.de> - 2012-08-01 11:27 +0200
            Re: SSE2 mhx@iae.nl (Marcel Hendrix) - 2012-08-01 20:23 +0200
            Re: SSE2 mhx@iae.nl (Marcel Hendrix) - 2012-08-05 21:00 +0200
    Re: SSE2 mhx@iae.nl (Marcel Hendrix) - 2012-07-28 15:28 +0200
      Re: SSE2 anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-31 14:29 +0000
  Re: SSE2 albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2012-07-27 16:31 +0000

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