Re: BN_MUL_MONT for ARM64 v8

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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@xxxxxxxxxx> 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@xxxxxxxxx
<mailto:vijay.chander@xxxxxxxxm>> 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@xxxxxxxxxxx
    <mailto:appro@xxxxxxxxxxx>> 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...



--
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Enjoy

Jakob
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