Re: use a non-locking initial test in TAS_SPIN on AArch64

Nathan Bossart <nathandbossart@gmail.com> writes:
> AFAICT TAS_SPIN() is only used for s_lock(), which doesn't appear to be
> used by LWLocks.  But I did retry my test from upthread without
> pg_stat_statements and was surprised to find a reproducible 4-6%
> regression.

On what hardware?

I just spent an hour beating on my M4 Pro (the 14-core variant)
and could not detect any outside-the-noise effect of this patch,
with or without pg_stat_statements loaded.  There does seem to be
a small fraction-of-a-percent-ish benefit.  But the run-to-run
variation with 60-second "pgbench -S" tests is a couple of percent,
so I can't say that that's real.

I do feel pretty sure that the patch doesn't hurt on this
class of hardware.

            regards, tom lane