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author | Anton Blanchard <anton@samba.org> | 2011-05-08 21:36:44 (GMT) |
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committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2011-05-19 04:30:42 (GMT) |
commit | f5f0307f42d39a51a925ca4841f76a2f2ea330ff (patch) | |
tree | 5dbaa4b57f6726537e1fd2ba6eb7c97854d85610 /arch/powerpc/mm/pgtable_64.c | |
parent | ba00ce1d6e08ad06f19f2ac53fd5c60bbe3fbeeb (diff) | |
download | linux-fsl-qoriq-f5f0307f42d39a51a925ca4841f76a2f2ea330ff.tar.xz |
powerpc: Improve scheduling of system call entry instructions
After looking at our system call path, Mary Brown suggested that we
should put all mfspr SRR* instructions before any mtspr SRR*.
To test this I used a very simple null syscall (actually getppid)
testcase at http://ozlabs.org/~anton/junkcode/null_syscall.c
I tested with the following changes against the pseries_defconfig:
CONFIG_VIRT_CPU_ACCOUNTING=n
CONFIG_AUDIT=n
to remove the overhead of virtual CPU accounting and syscall
auditing.
POWER6:
baseline: mean = 757.2 cycles sd = 2.108
modified: mean = 759.1 cycles sd = 2.020
POWER7:
baseline: mean = 411.4 cycles sd = 0.138
modified: mean = 404.1 cycles sd = 0.109
So we have 1.77% improvement on POWER7 which looks significant. The
POWER6 suggest a 0.25% slowdown, but the results are within 1
standard deviation and may be in the noise.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/mm/pgtable_64.c')
0 files changed, 0 insertions, 0 deletions