diff options
| author | Anton Blanchard | 2011-05-08 21:36:44 +0000 |
|---|---|---|
| committer | Benjamin Herrenschmidt | 2011-05-19 14:30:42 +1000 |
| commit | f5f0307f42d39a51a925ca4841f76a2f2ea330ff (patch) | |
| tree | 5dbaa4b57f6726537e1fd2ba6eb7c97854d85610 /arch/powerpc/kernel | |
| parent | ba00ce1d6e08ad06f19f2ac53fd5c60bbe3fbeeb (diff) | |
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/kernel')
| -rw-r--r-- | arch/powerpc/kernel/exceptions-64s.S | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 0ec3b42717d7..a85f4874cba7 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -211,11 +211,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) mr r9,r13 GET_PACA(r13) mfspr r11,SPRN_SRR0 - ld r12,PACAKBASE(r13) - ld r10,PACAKMSR(r13) - LOAD_HANDLER(r12, system_call_entry) - mtspr SPRN_SRR0,r12 mfspr r12,SPRN_SRR1 + ld r10,PACAKBASE(r13) + LOAD_HANDLER(r10, system_call_entry) + mtspr SPRN_SRR0,r10 + ld r10,PACAKMSR(r13) mtspr SPRN_SRR1,r10 rfid b . /* prevent speculative execution */ |