From: Anton Blanchard Date: Wed, 21 Jan 2015 01:27:38 +0000 (+1100) Subject: powerpc: Add 64bit optimised memcmp X-Git-Tag: fixes-v4.0-rc1~132^2~27 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=15c2d45d17418cc4a712608c78ff3b5f0583d83b;p=pandora-kernel.git powerpc: Add 64bit optimised memcmp I noticed ksm spending quite a lot of time in memcmp on a large KVM box. The current memcmp loop is very unoptimised - byte at a time compares with no loop unrolling. We can do much much better. Optimise the loop in a few ways: - Unroll the byte at a time loop - For large (at least 32 byte) comparisons that are also 8 byte aligned, use an unrolled modulo scheduled loop using 8 byte loads. This is similar to our glibc memcmp. A simple microbenchmark testing 10000000 iterations of an 8192 byte memcmp was used to measure the performance: baseline: 29.93 s modified: 1.70 s Just over 17x faster. v2: Incorporated some suggestions from Segher: - Use andi. instead of rdlicl. - Convert bdnzt eq, to bdnz. It's just duplicating the earlier compare and was a relic from a previous version. - Don't use cr5, we have plans to use that CR field for fast local atomics. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- Reading git-diff-tree failed