> On Aug 3, 2020, at 2:57 PM, Arvind Sankar <[email protected]> wrote: > > On Mon, Aug 03, 2020 at 12:40:22PM -0700, Nick Terrell wrote: >> From: Nick Terrell <[email protected]> >> >> This patch replaces all memcpy() calls with LZ4_memcpy() which calls >> __builtin_memcpy() so the compiler can inline it. >> >> LZ4 relies heavily on memcpy() with a constant size being inlined. In >> x86 and i386 pre-boot environments memcpy() cannot be inlined because >> memcpy() doesn't get defined as __builtin_memcpy(). >> >> An equivalent patch has been applied upstream so that the next import >> won't lose this change [1]. >> >> I've measured the kernel decompression speed using QEMU before and after >> this patch for the x86_64 and i386 architectures. The speed-up is about >> 10x as shown below. >> >> Code Arch Kernel Size Time Speed >> v5.8 x86_64 11504832 B 148 ms 79 MB/s >> patch x86_64 11503872 B 13 ms 885 MB/s >> v5.8 i386 9621216 B 91 ms 106 MB/s >> patch i386 9620224 B 10 ms 962 MB/s >> >> I also measured the time to decompress the initramfs on x86_64, i386, >> and arm. All three show the same decompression speed before and after, >> as expected. >> >> [1] https://github.com/lz4/lz4/pull/890 >> > > Hi Nick, would you be able to test the below patch's performance to > verify it gives the same speedup? It removes the #undef in misc.c which > causes the decompressors to not use the builtin version. It should be > equivalent to yours except for applying it to all the decompressors. > > Thanks.
I will measure it. I would expect it to provide the same speed up. It would be great to fix the problem for x86/i386 in general. But, I believe that this is also a problem for ARM, though I have a hard time measuring because I can’t get pre-boot print statements in QEMU. I will attempt to take a look at the assembly, because I’m fairly certain that memcpy() isn’t inlined in master. Even if we fix all the architectures, I would still like to merge the LZ4 patch. It seems like it is pretty easy to merge a patch that is a boot speed regression, because people aren’t actively measuring it. So I prefer a layered defense. Additionally, this is following upstream. At some point LZ4 will be imported from upstream and get an equivalent of this patch https://github.com/lz4/lz4/pull/890. Best, Nick
