Re: [PATCH] lz4: Fix kernel decompression speed

From: Arvind Sankar
Date: Mon Aug 03 2020 - 17:57:53 EST

On Mon, Aug 03, 2020 at 12:40:22PM -0700, Nick Terrell wrote:
> From: Nick Terrell <terrelln@xxxxxx>
> 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]

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.