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Re: SIMD Considered Harmful

From MitchAlsup <user5857@newsgrouper.org.invalid>
Newsgroups comp.arch
Subject Re: SIMD Considered Harmful
References <1790208006-5857@newsgrouper.org> <11920i6$29ujm$3@dont-email.me> <1790269788-5857@newsgrouper.org> <1194e2i$34hlg$8@dont-email.me>
Date 2026-09-25 00:41 +0000
Message-ID <1790296913-5857@newsgrouper.org> (permalink)

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Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> posted:

> On Thu, 24 Sep 2026 17:09:48 GMT, MitchAlsup wrote:
> 
> > Cray-vectors are arguably better at instruction addition than SIMD
> > and arguably inefficient when the element count of the vector is
> > small (4).
> 
> In the Cray docs somewhere, it said the break-even point where it is
> better to go through the setup of a vector instruction rather then
> execute individual scalar instructions for each set of operands is a
> vector length of just 2.

Yes, when memory was 20-odd cycles away--but a 5 GHz machine will find
memory 200 cycles away, not 20. That changes the break-even point (and
the number of elements in a vector register).

In addition, for vectors that short (4), caches work.

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Thread

SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-24 00:00 +0000
  Re: SIMD Considered Harmful Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-24 02:05 +0000
    Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-24 17:09 +0000
      Re: SIMD Considered Harmful Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-25 00:08 +0000
        Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-25 00:41 +0000
          Re: SIMD Considered Harmful Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-25 22:13 +0000
            Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-26 00:29 +0000
              Re: SIMD Considered Harmful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-09-26 06:41 +0000
                Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-26 18:23 +0000
                Re: SIMD Considered Harmful BGB <cr88192@gmail.com> - 2026-09-26 14:47 -0500
                Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-26 21:31 +0000
                Re: SIMD Considered Harmful BGB <cr88192@gmail.com> - 2026-09-26 20:56 -0500
                Re: SIMD Considered Harmful scott@slp53.sl.home (Scott Lurndal) - 2026-09-28 15:29 +0000
                Re: SIMD Considered Harmful BGB <cr88192@gmail.com> - 2026-09-28 17:39 -0500
                Re: SIMD Considered Harmful scott@slp53.sl.home (Scott Lurndal) - 2026-09-29 00:09 +0000
                Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-10-13 21:40 +0000
                Re: SIMD Considered Harmful Torbjorn Lindgren <tl@none.invalid> - 2026-09-29 17:01 +0000
                Re: SIMD Considered Harmful BGB <cr88192@gmail.com> - 2026-09-29 20:49 -0500
    Re: SIMD Considered Harmful BGB <cr88192@gmail.com> - 2026-09-24 15:04 -0500
  Re: SIMD Considered Harmful Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-09-24 07:54 -0700
    Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-24 19:48 +0000
      Re: SIMD Considered Harmful Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-09-24 13:58 -0700
        Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-24 22:24 +0000
          Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-25 00:27 +0000
          Re: SIMD Considered Harmful EricP <ThatWouldBeTelling@thevillage.com> - 2026-09-25 17:44 -0400
            Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-25 23:03 +0000
              Re: SIMD Considered Harmful EricP <ThatWouldBeTelling@thevillage.com> - 2026-09-27 11:33 -0400
                Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-28 00:04 +0000
                Re: SIMD Considered Harmful EricP <ThatWouldBeTelling@thevillage.com> - 2026-09-29 12:17 -0400
  Re: SIMD Considered Harmful Thomas Koenig <tkoenig@netcologne.de> - 2026-09-26 11:26 +0000
    Re: SIMD Considered Harmful Terje Mathisen <terje.mathisen@tmsw.no> - 2026-09-26 17:57 +0200
    Re: SIMD Considered Harmful BGB <cr88192@gmail.com> - 2026-09-26 13:52 -0500
      Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-26 21:24 +0000
    Re: SIMD Considered Harmful MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-26 21:16 +0000
  Re: SIMD Considered Harmful aph@littlepinkcloud.invalid - 2026-09-28 09:53 +0000

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