Re: Improving spin-lock implementation on ARM.

On Tue, Dec 1, 2020 at 3:44 PM Krunal Bauskar <krunalbauskar(at)gmail(dot)com> wrote:
> I have completed benchmarking with lse.
>
> Graph attached.

Thank you for benchmarking.

Now I agree with this comment by Tom Lane

> In general, I'm pretty skeptical of *all* the results posted so far on
> this thread, because everybody seems to be testing exactly one machine.
> If there's one thing that it's safe to assume about ARM, it's that
> there are a lot of different implementations; and this area seems very
> very likely to differ across implementations.

Different ARM implementations look too different. As you pointed out,
LSE is enabled in gcc-10 by default. I doubt we can accept a patch,
which gives benefits for specific platform and only when the compiler
isn't very modern. Also, we didn't cover all ARM planforms. Given
they are so different, we can't guarantee that patch doesn't cause
regression of some ARM. Additionally, the effect of the CAS patch
even for Kunpeng seems modest. It makes the drop off of TPS more
smooth, but it doesn't change the trend.

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Regards,
Alexander Korotkov