Maamoun TK <maamoun...@googlemail.com> writes:
> This implementation takes advantage of research made by Niels Möller to
> optimize GCM on PowerPC, this optimization yields a +27.7% performance
> boost on POWER8 over the previous implementation that was based on intel
> documents. The performance comparison is made by processing 4 blocks per
> loop without any further optimizations.
Hi, the patch didn't apply cleanly due to email line breaks (maybe try
posting as a text attachment next time?), but I've applied it
semi-manually, and pushed it to a branch ppc-gcm.
I gave it a test run on gcc112 in the gcc compile farm, and speedup of
gcm update seems to be 26 times(!) compared to the C version.
> I made some documentations between the lines but I suggest writing a
> document similar to the intel ones that go into more details and clarify
> the preference of this method.
Where would that documentation be published? In the Nettle manual, as
some IBM white paper, or as a more-or-less academic paper, e.g., on
arxiv? I will not be able to spend much time on writing, but I'd be
happy to review.
> I'm also curious if this method can also
> make a difference in other architectures like ARM, I'm planning to try it
> out for ARM to figure that out.
I have a sketch of ARM Neon code doing the equivalent of two vpmsumd,
with reasonable parallelism. Quite a lot of instructions needed.
Regards,
/Niels
> +C Alignment of gcm_key table elements, which is declared in gcm.h
> +define(`TableElemAlign', `0x100')
I still find this large constant puzzling. If I try
struct gcm_key key;
printf("sizeof (key): %zd, sizeof(key.h[0]): %zd\n", sizeof(key),
sizeof(key.h[0]));
(I added it to the start of test_main in gcm-test.c) and run on the
gcc112 machine, I get
sizeof (key): 4096, sizeof(key.h[0]): 16
Which is what I'd expect, with elements of size 16 bytes, not 256 bytes.
I haven't yet had the time to read the code carefully.
Regards,
/Niels
--
Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677.
Internet email is subject to wholesale government surveillance.
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