Messages in this thread |  | | Date | Wed, 6 Feb 2013 11:57:00 +0100 | Subject | Re: [PATCH 4/5] perf, x86: Support full width counting | From | Stephane Eranian <> |
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On Wed, Feb 6, 2013 at 1:27 AM, Andi Kleen <ak@linux.intel.com> wrote: > Here's an updated patch. I'm not reposting the full series. > Also cut down on cc to spare the innocents. > > --- > > perf, x86: Support full width counting v2 > > Recent Intel CPUs like Haswell and IvyBridge have a new alternative MSR > range for perfctrs that allows writing the full counter width. Enable this > range if the hardware reports it using a new capability bit. > > This lowers the overhead of perf stat slightly because it has to do less > interrupts to accumulate the counter value. On Haswell it also avoids some > problems with TSX aborting when the end of the counter range is reached. > > v2: Print the feature at boot
Tested okay for me. Reviewed-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Andi Kleen <ak@linux.intel.com> > > diff --git a/arch/x86/include/uapi/asm/msr-index.h b/arch/x86/include/uapi/asm/msr-index.h > index 433a59f..af41a77 100644 > --- a/arch/x86/include/uapi/asm/msr-index.h > +++ b/arch/x86/include/uapi/asm/msr-index.h > @@ -163,6 +163,9 @@ > #define MSR_KNC_EVNTSEL0 0x00000028 > #define MSR_KNC_EVNTSEL1 0x00000029 > > +/* Alternative perfctr range with full access. */ > +#define MSR_IA32_PMC0 0x000004c1 > + > /* AMD64 MSRs. Not complete. See the architecture manual for a more > complete list. */ > > diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h > index 1567b0d..ce2a863 100644 > --- a/arch/x86/kernel/cpu/perf_event.h > +++ b/arch/x86/kernel/cpu/perf_event.h > @@ -278,6 +278,7 @@ union perf_capabilities { > u64 pebs_arch_reg:1; > u64 pebs_format:4; > u64 smm_freeze:1; > + u64 fw_write:1; > }; > u64 capabilities; > }; > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c > index aa48048..06dcc0c 100644 > --- a/arch/x86/kernel/cpu/perf_event_intel.c > +++ b/arch/x86/kernel/cpu/perf_event_intel.c > @@ -2228,5 +2228,12 @@ __init int intel_pmu_init(void) > } > } > > + /* Support full width counters using alternative MSR range */ > + if (x86_pmu.intel_cap.fw_write) { > + x86_pmu.max_period = x86_pmu.cntval_mask; > + x86_pmu.perfctr = MSR_IA32_PMC0; > + pr_cont("full-width counters, "); > + } > + > return 0; > } > > -- > ak@linux.intel.com -- Speaking for myself only
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