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

Kan Liang
2014-10-19T22:07:47Z

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@intel.com>
Signed-off-by: Kan Liang <kan.liang@intel.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