[tip:perf/core] perf/x86/intel: Track number of events that use the LBR callstack

["tip-bot for Yan, Zheng" <tipbot@zytor.com>]

Commit-ID:  63f0c1d84196b712fe9de99a8514486ab416d517
Gitweb:     http://git.kernel.org/tip/63f0c1d84196b712fe9de99a8514486ab416d517
Author:     Yan, Zheng <zheng.z.yan@intel.com>
AuthorDate: Tue, 4 Nov 2014 21:56:04 -0500
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 18 Feb 2015 17:16:09 +0100

perf/x86/intel: Track number of events that use the LBR callstack

When enabling/disabling an event, check if the event uses the LBR
callstack feature, adjust the LBR callstack usage count accordingly.
Later patch will use the usage count to decide if LBR stack should
be saved/restored.

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/1415156173-10035-9-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index ac8279e..ac8e542 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -205,9 +205,15 @@ void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in)
 	}
 }
 
+static inline bool branch_user_callstack(unsigned br_sel)
+{
+	return (br_sel & X86_BR_USER) && (br_sel & X86_BR_CALL_STACK);
+}
+
 void intel_pmu_lbr_enable(struct perf_event *event)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct x86_perf_task_context *task_ctx;
 
 	if (!x86_pmu.lbr_nr)
 		return;
@@ -222,6 +228,12 @@ void intel_pmu_lbr_enable(struct perf_event *event)
 	}
 	cpuc->br_sel = event->hw.branch_reg.reg;
 
+	if (branch_user_callstack(cpuc->br_sel) && event->ctx &&
+					event->ctx->task_ctx_data) {
+		task_ctx = event->ctx->task_ctx_data;
+		task_ctx->lbr_callstack_users++;
+	}
+
 	cpuc->lbr_users++;
 	perf_sched_cb_inc(event->ctx->pmu);
 }
@@ -229,10 +241,17 @@ void intel_pmu_lbr_enable(struct perf_event *event)
 void intel_pmu_lbr_disable(struct perf_event *event)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct x86_perf_task_context *task_ctx;
 
 	if (!x86_pmu.lbr_nr)
 		return;
 
+	if (branch_user_callstack(cpuc->br_sel) && event->ctx &&
+					event->ctx->task_ctx_data) {
+		task_ctx = event->ctx->task_ctx_data;
+		task_ctx->lbr_callstack_users--;
+	}
+
 	cpuc->lbr_users--;
 	WARN_ON_ONCE(cpuc->lbr_users < 0);
 	perf_sched_cb_dec(event->ctx->pmu);