From: Vince Weaver Date: Thu, 1 Mar 2012 22:28:14 +0000 (-0500) Subject: perf/x86: Use rdpmc() rather than rdmsr() when possible in the kernel X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=c48b60538c3ba05a7a2713c4791b25405525431b;p=openwrt%2Fstaging%2Fblogic.git perf/x86: Use rdpmc() rather than rdmsr() when possible in the kernel The rdpmc instruction is faster than the equivelant rdmsr call, so use it when possible in the kernel. The perfctr kernel patches did this, after extensive testing showed rdpmc to always be faster (One can look in etc/costs in the perfctr-2.6 package to see a historical list of the overhead). I have done some tests on a 3.2 kernel, the kernel module I used was included in the first posting of this patch: rdmsr rdpmc Core2 T9900: 203.9 cycles 30.9 cycles AMD fam0fh: 56.2 cycles 9.8 cycles Atom 6/28/2: 129.7 cycles 50.6 cycles The speedup of using rdpmc is large. [ It's probably possible (and desirable) to do this without requiring a new field in the hw_perf_event structure, but the fixed events make this tricky. ] Signed-off-by: Vince Weaver Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1203011724030.26934@cl320.eecs.utk.edu Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index 43c2017347e7..000a4746c7ce 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -75,7 +75,7 @@ u64 x86_perf_event_update(struct perf_event *event) */ again: prev_raw_count = local64_read(&hwc->prev_count); - rdmsrl(hwc->event_base, new_raw_count); + rdpmcl(hwc->event_base_rdpmc, new_raw_count); if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, new_raw_count) != prev_raw_count) @@ -819,9 +819,11 @@ static inline void x86_assign_hw_event(struct perf_event *event, } else if (hwc->idx >= X86_PMC_IDX_FIXED) { hwc->config_base = MSR_ARCH_PERFMON_FIXED_CTR_CTRL; hwc->event_base = MSR_ARCH_PERFMON_FIXED_CTR0 + (hwc->idx - X86_PMC_IDX_FIXED); + hwc->event_base_rdpmc = (hwc->idx - X86_PMC_IDX_FIXED) | 1<<30; } else { hwc->config_base = x86_pmu_config_addr(hwc->idx); hwc->event_base = x86_pmu_event_addr(hwc->idx); + hwc->event_base_rdpmc = x86_pmu_addr_offset(hwc->idx); } } diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 45db49f64bb4..1ce887abcc5c 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -677,6 +677,7 @@ struct hw_perf_event { u64 last_tag; unsigned long config_base; unsigned long event_base; + int event_base_rdpmc; int idx; int last_cpu;