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Message-Id: <1395035856-15411-16-git-send-email-zheng.z.yan@intel.com>
Date: Mon, 17 Mar 2014 13:57:35 +0800
From: "Yan, Zheng" <zheng.z.yan@...el.com>
To: linux-kernel@...r.kernel.org
Cc: a.p.zijlstra@...llo.nl, mingo@...nel.org, acme@...radead.org,
eranian@...gle.com, andi@...stfloor.org,
"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: [PATCH v4 15/16] perf, x86: disable FREEZE_LBRS_ON_PMI when LBR operates in callstack mode
Due to a hardware bug of Haswell, LBR callstack does not work well with
FREEZE_LBRS_ON_PMI. If FREEZE_LBRS_ON_PMI is set, 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@...el.com>
---
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index bf8bdf9..5a6ea1c 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -138,7 +138,14 @@ static void __intel_pmu_lbr_enable(void)
wrmsrl(MSR_LBR_SELECT, cpuc->lbr_sel->config);
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 (!cpuc->lbr_sel || !(cpuc->lbr_sel->config & LBR_CALL_STACK))
+ debugctl |= DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
}
--
1.8.5.3
--
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