Commit-ID: cd1f11de69226cc7ce7e7f22bdab9010103ddaa6 Gitweb: http://git.kernel.org/tip/cd1f11de69226cc7ce7e7f22bdab9010103ddaa6 Author: Andi Kleen <a...@linux.intel.com> AuthorDate: Fri, 20 Mar 2015 10:11:24 -0700 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 2 Apr 2015 17:33:20 +0200
perf/x86/intel: Avoid rewriting DEBUGCTL with the same value for LBRs perf with LBRs on has a tendency to rewrite the DEBUGCTL MSR with the same value. Add a little optimization to skip the unnecessary write. Signed-off-by: Andi Kleen <a...@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: eran...@google.com Link: http://lkml.kernel.org/r/1426871484-21285-2-git-send-email-a...@firstfloor.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/kernel/cpu/perf_event_intel_lbr.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c index 3d53725..94e5b50 100644 --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c @@ -135,7 +135,7 @@ static void intel_pmu_lbr_filter(struct cpu_hw_events *cpuc); static void __intel_pmu_lbr_enable(bool pmi) { struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); - u64 debugctl, lbr_select = 0; + u64 debugctl, lbr_select = 0, orig_debugctl; /* * No need to reprogram LBR_SELECT in a PMI, as it @@ -147,6 +147,7 @@ static void __intel_pmu_lbr_enable(bool pmi) } rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); + orig_debugctl = debugctl; debugctl |= DEBUGCTLMSR_LBR; /* * LBR callstack does not work well with FREEZE_LBRS_ON_PMI. @@ -155,7 +156,8 @@ static void __intel_pmu_lbr_enable(bool pmi) */ if (!(lbr_select & LBR_CALL_STACK)) debugctl |= DEBUGCTLMSR_FREEZE_LBRS_ON_PMI; - wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); + if (orig_debugctl != debugctl) + wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); } static void __intel_pmu_lbr_disable(void) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
