Re: [PATCH][AARCH64] Set jump-align=4 for neoversen1

[Richard Sandiford <richard.sandiford@arm.com>]

Wilco Dijkstra <Wilco.Dijkstra@arm.com> writes:
> Hi Kyrill & Richard,
>
>> I was leaving this to others in case it was obvious to them.  On the
>> basis that silence suggests it wasn't, :-) could you go into more details?
>> Is it expected on first principles that jump alignment doesn't matter
>> for Neoverse N1, or is this purely based on experimentation?  If it's
>
> Jump alignment is set to 4 on almost all cores because higher values have
> a major codesize cost and yet give no performance gains.
>
> I suspect any core that set it higher has done so by accident rather than
> having benchmarked the cost/benefit.
>
>> expected, are we sure that the other "32:16" entries are still worthwhile?
>> When you say it doesn't make a difference in performance, does that mean
>> that no individual test's performance changed significantly, or just that
>> the aggregate score didn't?  Did you experiment with anything inbetween
>> the current 32:16 and 4, such as 32:8 or even 32:4?
>
> I mean there is no difference above the noise floor for any test you throw at it.

OK, great.  In that case, let's go with the patch as posted.

Thanks,
Richard

> I tried other alignments including 32:16, 32:12, 32:8 but all have a significant
> cost and zero benefit.
>
> Cheers,
> Wilco