On Fri, 2017-01-13 at 13:59 -0800, Jason Ekstrand wrote: > On Fri, Jan 13, 2017 at 11:22 AM, Vladislav Egorov <vegorov180@gmail. > com> wrote: > > 13.01.2017 19:51, Emil Velikov пишет: > > > From: Emil Velikov <emil.veli...@collabora.com> > > > > > > At the moment we support 5+ different implementations each with > > > varying > > > amount of bugs - from thread safely problems [1], to outright > > > broken > > > implementation(s) [2] > > > > > > In order to accommodate these we have 150+ lines of configure > > > script and > > > extra two configure toggles. Whist an actual implementation being > > > ~200loc and our current compat wrapping ~250. > > Yes, this is a problem. Especially given that at least one of those > implementations (openssl?) is something that a certain major game > distributor likes to hard-link into things causing interesting and > hard-to-debug problems. I am all for getting rid of the "piles of > different dependencies" approach. > > Also, something I would like to see (maybe a follow-on patch?) would > a change to the mesa internal API to be able to put the SHA context > on the stack and not need to malloc it. It's not really a memory or > cycle-saving thing so much as it leaves one fewer cleanup paths you > have to worry about. > > > > Let's not forget that different people use different code paths, > > > thus > > > effectively makes it harder to test and debug since the default > > > implementation is automatically detected. > > > > > > To minimise all these lovely experiences, import the "100% Public > > > Domain" OpenBSD sha1 implementation. Clearly document any changes > > > needed > > > to get building correctly, since many/most of those can be > > > upstreamed > > > making future syncs easier. > > > > > > > It can hurt performance. OpenSSL implementation is optimized for > > all thinkable architectures and it will use hardware SHA-1 > > instructions on newer CPUs. From https://github.com/openssl/openssl > > /blob/master/crypto/sha/asm/sha1-x86_64.pl : > > > > > Current performance is summarized in following table. Numbers are > > > CPU clock cycles spent to process single byte (less is better). > > > > > > x86_64 SSSE3 AVX[2] > > > P4 9.05 - > > > Opteron 6.26 - > > > Core2 6.55 6.05/+8% - > > > Westmere 6.73 5.30/+27% - > > > Sandy Bridge 7.70 6.10/+26% 4.99/+54% > > > Ivy Bridge 6.06 4.67/+30% 4.60/+32% > > > Haswell 5.45 4.15/+31% 3.57/+53% > > > Skylake 5.18 4.06/+28% 3.54/+46% > > > Bulldozer 9.11 5.95/+53% > > > VIA Nano 9.32 7.15/+30% > > > Atom 10.3 9.17/+12% > > > Silvermont 13.1(*) 9.37/+40% > > > Goldmont 8.13 6.42/+27% 1.70/+380%(**) > > > > Quick benchmark on my Haswell of the OpenBSD implementation > > compiled with GCC5 -O2: ~8 cycles per byte on 32-bit, ~7 cycles per > > byte on 64-bit. But Haswell is a very powerful CPU, on weaker CPUs > > the difference would be probably larger, especially on new CPUs > > that have SHA instruction set. > > Thanks for the numbers. It sounds like, on Haswell, the openSSL > implementation is about 2x as fast which is very useful to know. > However, this isn't on a super perf-critical path. We never use SHA1 > on any draw-time paths; we always use a simpler hash function in > those cases and reserve SHA1 for when we really don't want > collisions.
Actually the OpenGL shader cache uses it a draw time to find cached variants. I looked at pulling an implementation into Mesa a while ago but found the perf drop wasn't worth it. I really like the idea of having an internal implementation but I don't think we should dismiss performance so quickly it would be nice if we could hold this off until more testing can be done. > That said, it's a bit more critical than Emil makes it sound. A > typical Vulkan application may easily create 10k pipelines and each > of those will involve hashing at least about 100B of data (not > include the SPIR-V source). I doubt, however, that this is enough to > really cause a problem given how much other work goes into building a > pipeline. > > Unfortunately, the OpenSSL implementation, while fast, is one of the > ones that is causing problems. One of our favorite game distributors > likes to hard-link against openssl in some of their games and/or > libraries (not sure which). This means that, if mesa tries to > dynamically open libssl, you get mysterious crashes due to slight > differences between the system-installed version and the one that has > been linked into the game. This makes trying to use the OpenSSL > implementation a non-starter without being able to wholesale import > the implementation. > > Emil, I'm fine with this change. I haven't reviewed the details, but > my gut tells me we can eat the perf difference for now. Consider > that an Acked-by if you'd like but it would be good to have someone > review at least the build system stuff. > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
