Commit-ID: 2c70d0086e4e9e2440f0f78098090f32bde14277
Gitweb: http://git.kernel.org/tip/2c70d0086e4e9e2440f0f78098090f32bde14277
Author: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
AuthorDate: Tue, 4 Nov 2014 21:56:10 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 18 Feb 2015 17:16:13 +0100
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@xxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: eranian@xxxxxxxxxx
Cc: jolsa@xxxxxxxxxx
Link: http://lkml.kernel.org/r/1415156173-10035-15-git-send-email-kan.liang@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index a8b3f23..92a44fd 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -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);
}
--
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