On Mon, Aug 3, 2009 at 10:51 PM, Linus Torvalds<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > 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. It also >> shows very clearly why we default to the OpenSSL version over the Mozilla >> one. > > "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. Would there happen to be a SHA1 implementation around that can compute the SHA1 without first decompressing the data? Databases gain a lot of speed by using special algorithms that can directly operate on the compressed data. > > That said, under "normal" git usage models, the SHA1 costs are almost > invisible. So git-fsck is definitely a fairly unusual case that stresses > the SHA1 performance more than most git lods. > > Linus > -- > To unsubscribe from this list: send the line "unsubscribe git" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Jon Smirl jonsmirl@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html