linux-kernel - [PATCH 01/11] x86/intel_cqm: Modify hot cpu notification handling

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Date:	Wed,  9 Sep 2015 12:24:52 -0700
From:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
To:	vikas.shivappa@...el.com
Cc:	vikas.shivappa@...ux.intel.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...nel.org, tj@...nel.org, peterz@...radead.org,
	matt.fleming@...el.com, will.auld@...el.com,
	h.peter.anvin@...el.com, glenn.p.williamson@...el.com,
	kanaka.d.juvva@...el.com, bruce.schlobohm@...el.com
Subject: [PATCH 01/11] x86/intel_cqm: Modify hot cpu notification handling

 - In cqm_pick_event_reader, use the existing package<->core map instead
 of looping through all cpus in cqm_cpumask.

 - In intel_cqm_cpu_exit, use the same map instead of looping through
 all online cpus. In large systems with large number of cpus the time
 taken to loop may be expensive and also the time increases linearly.

Signed-off-by: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel_cqm.c | 34 +++++++++++++++---------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index 377e8f8..93e54ad 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -62,6 +62,12 @@ static LIST_HEAD(cache_groups);
  */
 static cpumask_t cqm_cpumask;
 
+/*
+ * Temporary cpumask used during hot cpu notificaiton handling. The usage
+ * is serialized by hot cpu locks.
+ */
+static cpumask_t tmp_cpumask;
+
 #define RMID_VAL_ERROR		(1ULL << 63)
 #define RMID_VAL_UNAVAIL	(1ULL << 62)
 
@@ -1244,15 +1250,13 @@ static struct pmu intel_cqm_pmu = {
 
 static inline void cqm_pick_event_reader(int cpu)
 {
-	int phys_id = topology_physical_package_id(cpu);
-	int i;
+	cpumask_and(&tmp_cpumask, &cqm_cpumask, topology_core_cpumask(cpu));
 
-	for_each_cpu(i, &cqm_cpumask) {
-		if (phys_id == topology_physical_package_id(i))
-			return;	/* already got reader for this socket */
-	}
-
-	cpumask_set_cpu(cpu, &cqm_cpumask);
+	/*
+	 * Pick a reader if there isn't one already.
+	 */
+	if (cpumask_empty(&tmp_cpumask))
+		cpumask_set_cpu(cpu, &cqm_cpumask);
 }
 
 static void intel_cqm_cpu_starting(unsigned int cpu)
@@ -1270,7 +1274,6 @@ static void intel_cqm_cpu_starting(unsigned int cpu)
 
 static void intel_cqm_cpu_exit(unsigned int cpu)
 {
-	int phys_id = topology_physical_package_id(cpu);
 	int i;
 
 	/*
@@ -1279,15 +1282,12 @@ static void intel_cqm_cpu_exit(unsigned int cpu)
 	if (!cpumask_test_and_clear_cpu(cpu, &cqm_cpumask))
 		return;
 
-	for_each_online_cpu(i) {
-		if (i == cpu)
-			continue;
+	cpumask_and(&tmp_cpumask, topology_core_cpumask(cpu), cpu_online_mask);
+	cpumask_clear_cpu(cpu, &tmp_cpumask);
+	i = cpumask_any(&tmp_cpumask);
 
-		if (phys_id == topology_physical_package_id(i)) {
-			cpumask_set_cpu(i, &cqm_cpumask);
-			break;
-		}
-	}
+	if (i < nr_cpu_ids)
+		cpumask_set_cpu(i, &cqm_cpumask);
 }
 
 static int intel_cqm_cpu_notifier(struct notifier_block *nb,
-- 
1.9.1

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