Commit 069e0c3c authored by Andi Kleen's avatar Andi Kleen Committed by Ingo Molnar

perf/x86/intel: Support full width counting

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.

Currently the perf code queries CPUID to get the counter width,
and sign extends the counter values as needed. The traditional
PERFCTR MSRs always limit to 32bit, even though the counter
internally is larger (usually 48 bits on recent CPUs)

When the new capability is set use the alternative range which
do not have these restrictions.

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.

( See the patch "perf/x86/intel: Avoid checkpointed counters
  causing excessive TSX aborts" for more details. )
Signed-off-by: default avatarAndi Kleen <>
Reviewed-by: default avatarStephane Eranian <>
Acked-by: default avatarPeter Zijlstra <>
Link: default avatarIngo Molnar <>
parent 0c4df02d
......@@ -170,6 +170,9 @@
#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. */
......@@ -310,6 +310,11 @@ union perf_capabilities {
u64 pebs_arch_reg:1;
u64 pebs_format:4;
u64 smm_freeze:1;
* PMU supports separate counter range for writing
* values > 32bit.
u64 full_width_write:1;
u64 capabilities;
......@@ -2340,5 +2340,12 @@ __init int intel_pmu_init(void)
/* Support full width counters using alternative MSR range */
if (x86_pmu.intel_cap.full_width_write) {
x86_pmu.max_period = x86_pmu.cntval_mask;
x86_pmu.perfctr = MSR_IA32_PMC0;
pr_cont("full-width counters, ");
return 0;
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