Re: rep movsb vs. simpler instructions for memcpy/memmove

On Thu, 13 Mar 2025 14:29:54 +0000, Michael S wrote:

On Thu, 13 Mar 2025 02:34:11 -0000 (UTC)
Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
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On Thu, 13 Mar 2025 00:49:47 +0000, MitchAlsup1 wrote:
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On Thu, 13 Mar 2025 0:03:51 +0000, Lawrence D'Oliveiro wrote:
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On Wed, 12 Mar 2025 17:44:11 +0000, MitchAlsup1 wrote:
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My 66000 has MM memmove as an instruction (4-bytes) always
optimal, no checking required.

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Presumably interruptible and resumable ...

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Yep; but also include able to take exceptions.

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So you have a VAX-style “first part done” processor status bit? And
you use architectural registers to save/restore the state of an
instruction in progress at the time of an interrupt?

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According to my understanding, no and no.
Mitch has instruction

s/instruction/hardware means/

                      that saves architectural+microarchitectural
context in memory and any interrupt or exception has to use it.

Technically, you don't have to use it; it happens automatically.
In one instant you are executing thread[k] in core[j], the next
instant you are executing thread[m] in core[j] without SW over-
head. Thread[j] and [k] are not related and share no state.

Architectural part of saved buffer is documented. Microarchitectural
part, apart from its size, not so much.
That is, according to my understanding. Take it with amount of salt you
find appropriate.