On Tue, 28 Oct 2025 at 09:42, Kuniyuki Iwashima <[email protected]> wrote:
>
> This is the Zen 2 platform, so probably the stac/clac cost will be
> more expensive than you expect on Zen 5.
Yeah, clac/stac are horrenously expensive on Zen 2. I think they are
microcoded - and not the fast kind - so effectively serializing.
They got enormously faster and pipelined in later Zen microarchitectures.
Sadly, Agner Fog doesn't do timings on those instructions, and I
haven't found any other place that has some overview of the
performance on different microarchitectures.
Linus
