[openssl-users] BN_MUL_MONT for ARM64 v8

Andy Polyakov appro at openssl.org
Tue Feb 7 19:07:37 UTC 2017

> A72 is running 1GHz compared to x86 at 2.1Ghz. So that should hopefully
> get down to -1:5.

And Mongoose will take you to ~1:2.5 (scaled to same frequency that is).
Which I'd say is a fair result. Well, still could have been a bit
better, but it's not unreasonable given ISA differences. Keep in mind
that presented x86_64 result is for code utilizing Intel-specific code

> There is no L3 cache on the A72 eval board and performance counters do
> show 9x more DRAM accesses for ARM compared to x86.

This is unexpected, because it takes *less* references to memory to
perform it on ARMv8. Because it has larger register bank. And cache
requirement is not that high for L3 to kick in... But at any case memory
is not bottleneck here...

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