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

Hi~

Upon closer inspection, I noticed that we don't implement a custom
> TAS_SPIN() for this architecture, so I quickly hacked together the attached
> patch and ran a couple of benchmarks that stressed the spinlock code.  I
> found no discussion about TAS_SPIN() on ARM in the archives, but I did
> notice that the initial AArch64 support was added [0] before x86_64 started
> using a non-locking test [1].
>
It reminds me of a discussion about improving spinlock performance on ARM
in 2020 [0], though the discussion is about CAS and TAS, not TAS_SPIN()
itself.


>     tps = 74135.100891 (without initial connection time)
>     tps = 549462.785554 (without initial connection time)

The result looks great, but the discussion in [0] shows that the result may
vary among different ARM chips. Could you provide the chip model of this
test? So that we can do a cross validation of this patch. Not sure if
compiler
version is necessary too. I'm willing to test it on Alibaba Cloud Yitian 710
if I have time.

[0]
https://www.postgresql.org/message-id/flat/CAPpHfdsGqVd6EJ4mr_RZVE5xSiCNBy4MuSvdTrKmTpM0eyWGpg%40mail.gmail.com#ca3c4255b627826eb6d03b2d4dcf4ead

- Regards
Jingtang