069e0c3c40
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: Andi Kleen <ak@linux.intel.com> Reviewed-by: Stephane Eranian <eranian@google.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1372173153-20215-1-git-send-email-andi@firstfloor.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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