[openssl-users] BN_MUL_MONT for ARM64 v8

[Mike Mohr]

Of course OpenSSL contains hand-optimized assembly routines.  However, GMP
has been around since at least 1993 and the library specifically targets
heavily optimized multiple precision arithmetic.  OpenSSL is a TLS/SSL
toolkit, and necessarily focuses on implementing SSL/TLS correctly - I'd
argue that the bigint subsystem is almost tangential to the other parts of
any SSL library.  A less optimized bigint subsystem should be reasonably
expected.  I would be surprised if the native bigint code could compete
against GMP performance-wise, even when OpenSSL's optimized assembly code
is used.  I haven't benchmarked OpenSSL's bigint subsystem and would be
interested in seeing a comparison against a correctly configured GMP.

On Tue, Feb 7, 2017 at 4:46 PM, Jakob Bohm <jb-openssl at wisemo.com> wrote:

> OpenSSL also has a lot of handwritten assembly language for ARM,
> x86 etc.  Most of it written by Andy Polyakov.
>
> His response about what can and cannot be done on various ARM CPU
> models is most probably a result of this work.
>
> Also, OpenSSL has a more permissive license than the GMP, so using
> GMP in OpenSSL would cause problems for many OpenSSL using
> applications.
>
> On 08/02/2017 00:31, Mike Mohr wrote:
>
>> Have you considered using GMP as a big integer backed for openssl?  It
>> has support for several arm variants using handwritten assembly code
>> and the developers go to great lengths to find optimize runtime on all
>> supported platforms.
>>
>> On Feb 7, 2017 2:26 PM, "Vijay Chander" <vijay.chander at gmail.com
>> <mailto:vijay.chander at gmail.com>> wrote:
>>
>>     Andy,
>>        1:2.5 is pretty in my opinion for ARM !
>>
>>        We  will check out Mongoose.
>>
>>        Hmm - will try to get to the bottom of those cache misses (at a
>>     lower priority).
>>
>>     Thanks,
>>     -vijay
>>
>>
>>     On Tue, Feb 7, 2017 at 11:07 AM, Andy Polyakov <appro at openssl.org
>>     <mailto:appro at openssl.org>> wrote:
>>
>>         > 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
>>         extensions.
>>
>>         > 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...
>>
>>
>
> --
> Jakob Bohm, CIO, partner, WiseMo A/S. https://www.wisemo.com
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>
> Enjoy
>
> Jakob
> --
> Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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