Commit 2c70d008 authored Nov 04, 2014 by Yan, Zheng Committed by Ingo Molnar Feb 18, 2015

perf/x86/intel: Disable FREEZE_LBRS_ON_PMI when LBR operates in callstack mode



LBR callstack is designed for PEBS, It does not work well with
FREEZE_LBRS_ON_PMI for non PEBS event. If FREEZE_LBRS_ON_PMI is set for
non PEBS event, PMIs near call/return instructions may cause superfluous
increase/decrease of LBR_TOS.

This patch modifies __intel_pmu_lbr_enable() to not enable
FREEZE_LBRS_ON_PMI when LBR operates in callstack mode. We currently
don't use LBR callstack to capture kernel space callchain, so disabling
FREEZE_LBRS_ON_PMI should not be a problem.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: eranian@google.com
Cc: jolsa@redhat.com
Link: http://lkml.kernel.org/r/1415156173-10035-15-git-send-email-kan.liang@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4b854900

arch/x86/kernel/cpu/perf_event_intel_lbr.c

+13 −4

Original line number	Diff line number	Diff line
		@@ -131,14 +131,23 @@ static void intel_pmu_lbr_filter(struct cpu_hw_events *cpuc);

		static void __intel_pmu_lbr_enable(void)
		{
		u64 debugctl;
		struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
		u64 debugctl, lbr_select = 0;

		if (cpuc->lbr_sel)
		wrmsrl(MSR_LBR_SELECT, cpuc->lbr_sel->config);
		if (cpuc->lbr_sel) {
		lbr_select = cpuc->lbr_sel->config;
		wrmsrl(MSR_LBR_SELECT, lbr_select);
		}

		rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
		debugctl \|= (DEBUGCTLMSR_LBR \| DEBUGCTLMSR_FREEZE_LBRS_ON_PMI);
		debugctl \|= DEBUGCTLMSR_LBR;
		/*
		* LBR callstack does not work well with FREEZE_LBRS_ON_PMI.
		* If FREEZE_LBRS_ON_PMI is set, PMI near call/return instructions
		* may cause superfluous increase/decrease of LBR_TOS.
		*/
		if (!(lbr_select & LBR_CALL_STACK))
		debugctl \|= DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
		wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
		}