Messages in this thread | | | Subject | Re: [PATCH] perf_event use rdpmc rather than rdmsr when possible in kernel | From | Peter Zijlstra <> | Date | Mon, 27 Feb 2012 12:39:22 +0100 |
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On Mon, 2012-02-20 at 17:38 -0500, Vince Weaver wrote:
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index 5adce10..5550047 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -85,7 +85,7 @@ 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); > + new_raw_count=native_read_pmc(hwc->event_base_rdpmc);
That really wants to be rdpmc(), bypassing paravirt like that isn't nice.
> > if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, > new_raw_count) != prev_raw_count) > @@ -768,9 +768,11 @@ 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 abb2776..432ac69 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -562,6 +562,7 @@ struct hw_perf_event { > u64 last_tag; > unsigned long config_base; > unsigned long event_base; > + unsigned long event_base_rdpmc;
We could make that unsigned int, the SDM explicitly states rdmsr/wrmsr/rdpmc take ECX (and ignore the upper 32bits RCX).
> int idx; > int last_cpu; > struct hw_perf_event_extra extra_reg;
But yeah, avoiding the extra variable will add a conditional and extra instructions to the rdpmc path.
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