Re: x86 SHA1: Faster than OpenSSL
- From
- Andy Polyakov <appro@fy.chalmers.se>
- Date
- Aug 18, 2009, 21:50 UTC
- Message-ID
- <4A8B2216.6080607@fy.chalmers.se>
- In-Reply-To
- <alpine.LFD.2.01.0908031938280.3270@localhost.localdomain>
Show 12 quoted lines
> On Mon, 3 Aug 2009, Linus Torvalds wrote: >> The thing that I'd prefer is simply >> >> git fsck --full >> >> on the Linux kernel archive. For me (with a fast machine), it takes about >> 4m30s with the OpenSSL SHA1, and takes 6m40s with the Mozilla SHA1 (ie >> using a NO_OPENSSL=1 build). >> >> So that's an example of a load that is actually very sensitive to SHA1 >> performance (more so than _most_ git loads, I suspect), and at the same >> time is a real git load rather than some SHA1-only microbenchmark.
I couldn't agree more that real-life benchmarks are of greater value than specific algorithm micro-benchmark. And given the provided profiling data one can argue that +17% (or my +12%) improvement on micro-benchmark aren't really worth bothering about. But it's kind of sport [at least for me], so don't judge too harshly:-)
>> It also >> shows very clearly why we default to the OpenSSL version over the Mozilla >> one.
As George implicitly mentioned most OpenSSL assembler modules are available under more permissive license and if there is interest I'm ready to assist...
Show 17 quoted lines
> "perf report --sort comm,dso,symbol" profiling shows the following for > 'git fsck --full' on the kernel repo, using the Mozilla SHA1: > > 47.69% git /home/torvalds/git/git [.] moz_SHA1_Update > 22.98% git /lib64/libz.so.1.2.3 [.] inflate_fast > 7.32% git /lib64/libc-2.10.1.so [.] __GI_memcpy > 4.66% git /lib64/libz.so.1.2.3 [.] inflate > 3.76% git /lib64/libz.so.1.2.3 [.] adler32 > 2.86% git /lib64/libz.so.1.2.3 [.] inflate_table > 2.41% git /home/torvalds/git/git [.] lookup_object > 1.31% git /lib64/libc-2.10.1.so [.] _int_malloc > 0.84% git /home/torvalds/git/git [.] patch_delta > 0.78% git [kernel] [k] hpet_next_event > > so yeah, SHA1 performance matters. Judging by the OpenSSL numbers, the > OpenSSL SHA1 implementation must be about twice as fast as the C version > we use.
And given /lib64 path this is 64-bit C compiler-generated code compared to 32-bit assembler? Either way in this context I have extra comment addressing previous subscriber, Mark Lodato, who effectively wondered how would 64-bit assembler compare to 32-bit one. First of all there *is* even 64-bit assembler version. But as SHA1 is essentially 32-bit algorithm, 64-bit implementation is only nominally faster, +20% at most. Faster thanks to larger register bank facilitating more efficient instruction scheduling.
Cheers. A.