[SRU,D/OEM-OSP1-B,v2,07/20] perf/x86/lbr: Avoid reading the LBRs when adaptive PEBS handles them
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Message ID 20191127080028.200261-8-vicamo.yang@canonical.com
State New
Headers show
Series
  • Add perf support for Comet Lake/Ice Lake CPU
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Commit Message

You-Sheng Yang Nov. 27, 2019, 8 a.m. UTC
From: Andi Kleen <ak@linux.intel.com>

With adaptive PEBS the CPU can directly supply the LBR information,
so we don't need to read it again. But the LBRs still need to be
enabled. Add a special count to the cpuc that distinguishes these
two cases, and avoid reading the LBRs unnecessarily when PEBS is
active.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Cc: jolsa@kernel.org
Link: https://lkml.kernel.org/r/20190402194509.2832-7-kan.liang@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit d3617b98b04583df222f34992e65712862a77bf1)
Signed-off-by: You-Sheng Yang <vicamo.yang@canonical.com>
---
 arch/x86/events/intel/lbr.c  | 13 ++++++++++++-
 arch/x86/events/perf_event.h |  1 +
 2 files changed, 13 insertions(+), 1 deletion(-)

Patch
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diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 58889f952959..b8cac31f089c 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -488,6 +488,8 @@  void intel_pmu_lbr_add(struct perf_event *event)
 	 * be 'new'. Conversely, a new event can get installed through the
 	 * context switch path for the first time.
 	 */
+	if (x86_pmu.intel_cap.pebs_baseline && event->attr.precise_ip > 0)
+		cpuc->lbr_pebs_users++;
 	perf_sched_cb_inc(event->ctx->pmu);
 	if (!cpuc->lbr_users++ && !event->total_time_running)
 		intel_pmu_lbr_reset();
@@ -507,8 +509,11 @@  void intel_pmu_lbr_del(struct perf_event *event)
 		task_ctx->lbr_callstack_users--;
 	}
 
+	if (x86_pmu.intel_cap.pebs_baseline && event->attr.precise_ip > 0)
+		cpuc->lbr_pebs_users--;
 	cpuc->lbr_users--;
 	WARN_ON_ONCE(cpuc->lbr_users < 0);
+	WARN_ON_ONCE(cpuc->lbr_pebs_users < 0);
 	perf_sched_cb_dec(event->ctx->pmu);
 }
 
@@ -658,7 +663,13 @@  void intel_pmu_lbr_read(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
-	if (!cpuc->lbr_users)
+	/*
+	 * Don't read when all LBRs users are using adaptive PEBS.
+	 *
+	 * This could be smarter and actually check the event,
+	 * but this simple approach seems to work for now.
+	 */
+	if (!cpuc->lbr_users || cpuc->lbr_users == cpuc->lbr_pebs_users)
 		return;
 
 	if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_32)
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 84d225cfaacc..cd6984ba50a6 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -234,6 +234,7 @@  struct cpu_hw_events {
 	 * Intel LBR bits
 	 */
 	int				lbr_users;
+	int				lbr_pebs_users;
 	struct perf_branch_stack	lbr_stack;
 	struct perf_branch_entry	lbr_entries[MAX_LBR_ENTRIES];
 	struct er_account		*lbr_sel;