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Re: SIMD Considered Harmful

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BGB <cr88192@gmail.com> posted:

> On 9/26/2026 1:23 PM, MitchAlsup wrote:
> > 
> > anton@mips.complang.tuwien.ac.at (Anton Ertl) posted:
> > 
> >> MitchAlsup <user5857@newsgrouper.org.invalid> writes:
> >>> When memory was 20-cycles away, a 64-entry vector register could absorb
> >>> the entire latency 3 times. If memory is 200-cycles away, a 64-entry
> >>> vector register can absorb only 1/3 of a memory latency.
> >>
> >> Modern microarchitectures have prefetchers and caches for absorbing
> >> DRAM latency.
> >>
> >> BTW, 200 cycles at 5 GHz would mean 40ns.  I have never seen such a
> >> low latency.  The best was around 50ns, but 70ns-100ns is more
> >> typical.
> > 
> > I wanted to use 300 cycles (60 ns); but felt people would think I
> > was over playing my hand.
> > 
> 
> Well, for me, it is like the weirdness of seeing videos where people 
> claim read/write speeds on NVMe SSD's that seem to encroach on the 
> territory I see when benchmarking "memcpy()" style operations.

The well published X-zillion 4KB random reads per second does not have
any of those 4KB pages touched by CPU instructions ?? So, it measures 
only the PCIe perf and not memory perf.
 
> Well, and much faster than the 300 MB/s I see with a SATA SSD (where 
> both the SSD and MOBO support SATA3, which theoretically has a higher 
> limit, but in testing I see 300MB/s, or the SATA2 limit).

It is kind of sad that a single link PCIe 5.0 can transfer all the data
that 10-to-20 300MB SATA drives can produce/consume.
 
> But, for bulk RAM copy (within a single core), seemingly the CPUs cap 
> out at around 3.4 GB/sec.

One cache line every 4-8 cycles. Kind of sad, here, too. We should have 
on-Die interconnects of 2×512-bits per cycle per step on the on-Die
interconnect (Cache line, both ways, for each node).
 

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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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