On Sun, Jun 10, 2007 at 12:47:19PM -0400, Benjamin Gilbert wrote: > Matt Mackall wrote: > >On Sat, Jun 09, 2007 at 08:33:25PM -0400, Benjamin Gilbert wrote: > >>It's not just the loop unrolling; it's the register allocation and > >>spilling. For comparison, I built SHATransform() from the > >>drivers/char/random.c in 2.6.11, using gcc 3.3.5 with -O2 and > >>SHA_CODE_SIZE == 3 (i.e., fully unrolled); I'm guessing this is pretty > >>close to what you tested back then. The resulting code is 49% MOV > >>instructions, and 80% of *those* involve memory. gcc4 is somewhat > >>better, but it still spills a whole lot, both for the 2.6.11 unrolled > >>code and for the current lib/sha1.c. > > > >Wait, your benchmark is comparing against the unrolled code? > > No, it's comparing the current lib/sha1.c to the optimized code in the > patch. I was just pointing out that the unrolled code you were likely > testing against, back then, may not have been very good. (Though I > assumed that you were talking about the unrolled code in random.c, not > the code in CryptoAPI, so that might change the numbers some. It > appears from the post you linked below that the unrolled CryptoAPI code > still beat the rolled version?) That predates lib/sha1.c by a while. > >How big is the -code- footprint? > > About 3700 bytes for the 32-bit version of sha_transform(). lib/sha1.c's footprint is... 621 bytes today. Huh. That's up from 466 bytes when it was introduced and no one's touched it: http://search.luky.org/ML/linux-kernel.2005/msg06648.html Stupid compilers. But anyway. Cache footprint matters. The two big users of SHA1 in the kernel are /dev/random and IPSec, both of which typically operate on small chunks of data. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
