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a9514dc69d
Version 2.06 of the POWER ISA introduced enhanced touch instructions, allowing us to specify a number of attributes including the length of a stream. This patch adds a software stream for both loads and stores in the POWER7 copy_tofrom_user loop. Since the setup is quite complicated and we have to use an eieio to ensure correct ordering of the "GO" command we only do this for copies above 4kB. To quantify any performance improvements we need a working set bigger than the caches so we operate on a 1GB file: # dd if=/dev/zero of=/tmp/foo bs=1M count=1024 And we compare how fast we can read the file: # dd if=/tmp/foo of=/dev/null bs=1M before: 7.7 GB/s after: 9.6 GB/s A 25% improvement. The worst case for this patch will be a completely L1 cache contained copy of just over 4kB. We can test this with the copy_to_user testcase we used to tune copy_tofrom_user originally: http://ozlabs.org/~anton/junkcode/copy_to_user.c # time ./copy_to_user2 -l 4224 -i 10000000 before: 6.807 s after: 6.946 s A 2% slowdown, which seems reasonable considering our data is unlikely to be completely L1 contained. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> |
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