[PATCH] aarch64: Optimized memcmp for medium to large sizes

[Siddhesh Poyarekar]

On Monday 12 February 2018 07:41 PM, Siddhesh Poyarekar wrote:
> On Monday 12 February 2018 05:07 PM, Marcus Shawcroft wrote:
>> Thanks for sharing the performance numbers on these two
>> u-architectures.  Have you looked at the impact of this patch on
>> performance of the various other aarch64 u-architectures?  If so
>> please share your findings.
> 
> I don't have ready access to any other u-arch (unless you want me to
> share more performance numbers on other Qualcomm cores, but I suspect
> you don't ;)), but I'll ask around and let you know.

Sorry it took me a bit long but I was finally able to get my hands on a
HiKey960 (which has A73 and A53 cores) and set it up.  I isolated
bench-memcmp on each of those types of cores one at a time and both do
fairly well with the new memcmp.

On the a73 core, performance of the 128 byte to 4K compares take up to
11%-33% less time.  On the a53 core, the same range takes between 8%-30%
less time.  Numbers for smaller sizes are unstable and fluctuating
between -30% and +30% for the same inputs.  I have not found a way to
stabilize these numbers in the benchmark.

So now we have numbers for 4 micro-architectures, all showing positive
gains for medium sizes and non-significant changes in performance for
the smaller sizes.

Siddhesh