On Tue, Aug 04, 2020 at 10:32:36AM +0200, Pavel Machek wrote: > Hi! > > > >> 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. > > > Layered defense against performance-only problem, happening on > emulation-only? > > IMO that's a bit of overkill. > > Best regards, > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) > http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
Why would it be emulation-only? QEMU is just being used for ease of testing, but the performance impact should be similar on bare metal. Thanks.
