linux-kernel - [PATCH V6 13/17] perf, x86: enable LBR callstack when recording callchain

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Date:	Sun, 19 Oct 2014 17:55:08 -0400
From:	Kan Liang <kan.liang@...el.com>
To:	a.p.zijlstra@...llo.nl, eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, paulus@...ba.org,
	acme@...nel.org, jolsa@...hat.com, ak@...ux.intel.com,
	Kan Liang <kan.liang@...el.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: [PATCH V6 13/17] perf, x86: enable LBR callstack when recording callchain

Only enable LBR callstack when user requires fp callgraph. The feature
is not available when PERF_SAMPLE_BRANCH_STACK or PERF_SAMPLE_STACK_USER
is required.
Also, this feature only affects how to get user callchain. The kernel
callchain is always got by frame pointers.

Signed-off-by: Yan, Zheng <zheng.z.yan@...el.com>
Signed-off-by: Kan Liang <kan.liang@...el.com>
---
 arch/x86/kernel/cpu/perf_event.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 9656b9e..b3256a3 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -424,10 +424,24 @@ int x86_pmu_hw_config(struct perf_event *event)
 			if (!event->attr.exclude_kernel)
 				*br_type |= PERF_SAMPLE_BRANCH_KERNEL;
 		}
-	}
+	} else if (x86_pmu_has_lbr_callstack() &&
+		   (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
+		   !(event->attr.sample_type & PERF_SAMPLE_STACK_USER) &&
+		   !has_branch_stack(event) &&
+		   !event->attr.exclude_user &&
+		   (event->attach_state & PERF_ATTACH_TASK)) {
+		/*
+		 * user did not specify branch_sample_type,
+		 * try using the LBR call stack facility to
+		 * record call chains of user program.
+		 */
+		event->attr.branch_sample_type =
+			PERF_SAMPLE_BRANCH_USER |
+			PERF_SAMPLE_BRANCH_CALL_STACK;
 
-	if (event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_CALL_STACK)
+		/* needs PMU specific data to save LBR stack */
 		event->attach_state |= PERF_ATTACH_TASK_DATA;
+	}
 
 	/*
 	 * Generate PMC IRQs:
-- 
1.8.3.2

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