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authorIngo Molnar <mingo@elte.hu>2008-11-08 16:19:55 +0100
committerIngo Molnar <mingo@elte.hu>2008-11-08 16:48:19 +0100
commit0d12cdd5f883f508d33b85c1bae98fa28987c8c7 (patch)
treee07bb1f9ef49062fbd9817fe41cab66964bedf03 /arch/x86/include/asm/tsc.h
parent52c642f33b14bfa1b00ef2b68296effb34a573f3 (diff)
downloadop-kernel-dev-0d12cdd5f883f508d33b85c1bae98fa28987c8c7.zip
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sched: improve sched_clock() performance
in scheduler-intense workloads native_read_tsc() overhead accounts for 20% of the system overhead: 659567 system_call 41222.9375 686796 schedule 435.7843 718382 __switch_to 665.1685 823875 switch_mm 4526.7857 1883122 native_read_tsc 55385.9412 9761990 total 2.8468 this is large part due to the rdtsc_barrier() that is done before and after reading the TSC. But sched_clock() is not a precise clock in the GTOD sense, using such barriers is completely pointless. So remove the barriers and only use them in vget_cycles(). This improves lat_ctx performance by about 5%. Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/include/asm/tsc.h')
-rw-r--r--arch/x86/include/asm/tsc.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 38ae163..9cd83a8 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -34,6 +34,8 @@ static inline cycles_t get_cycles(void)
static __always_inline cycles_t vget_cycles(void)
{
+ cycles_t cycles;
+
/*
* We only do VDSOs on TSC capable CPUs, so this shouldnt
* access boot_cpu_data (which is not VDSO-safe):
@@ -42,7 +44,11 @@ static __always_inline cycles_t vget_cycles(void)
if (!cpu_has_tsc)
return 0;
#endif
- return (cycles_t)__native_read_tsc();
+ rdtsc_barrier();
+ cycles = (cycles_t)__native_read_tsc();
+ rdtsc_barrier();
+
+ return cycles;
}
extern void tsc_init(void);
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