linux-kernel - [PATCH 03/10] x86/intel_rapl: Modify hot cpu notification handling for RAPL

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Date:	Thu,  4 Jun 2015 17:01:30 -0700
From:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	vikas.shivappa@...el.com, x86@...nel.org, hpa@...or.com,
	tglx@...utronix.de, mingo@...nel.org, tj@...nel.org,
	peterz@...radead.org, matt.fleming@...el.com, will.auld@...el.com,
	kanaka.d.juvva@...el.com, vikas.shivappa@...ux.intel.com
Subject: [PATCH 03/10] x86/intel_rapl: Modify hot cpu notification handling for RAPL

This patch modifies the hot cpu notification handling in
Intel Running Average Power Limit(RAPL) driver.

 - to add a cpu reader to the rapl_cpumask(which has one cpu per package
     set) it uses the existing package<->core map instead of looping
 through all cpus in rapl_cpumask.
 - to search for the next online sibling during hot cpu exit, it uses
 the cpumask_any_online_but instead of looping all online cpus. In
 large systems with large number of cpus the time taken to loop may be
 expensive and also the time increase linearly.

Signed-off-by: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel_rapl.c | 27 ++++++++++-----------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_rapl.c b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
index 358c54a..987383e 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_rapl.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
@@ -524,18 +524,14 @@ static struct pmu rapl_pmu_class = {
 static void rapl_cpu_exit(int cpu)
 {
 	struct rapl_pmu *pmu = per_cpu(rapl_pmu, cpu);
-	int i, phys_id = topology_physical_package_id(cpu);
 	int target = -1;
+	int i;
 
 	/* find a new cpu on same package */
-	for_each_online_cpu(i) {
-		if (i == cpu)
-			continue;
-		if (phys_id == topology_physical_package_id(i)) {
-			target = i;
-			break;
-		}
-	}
+	i = cpumask_any_online_but(topology_core_cpumask(cpu), cpu);
+	if (i < nr_cpu_ids)
+		target = i;
+
 	/*
 	 * clear cpu from cpumask
 	 * if was set in cpumask and still some cpu on package,
@@ -557,15 +553,12 @@ static void rapl_cpu_exit(int cpu)
 
 static void rapl_cpu_init(int cpu)
 {
-	int i, phys_id = topology_physical_package_id(cpu);
+	struct cpumask tmp;
 
-	/* check if phys_is is already covered */
-	for_each_cpu(i, &rapl_cpu_mask) {
-		if (phys_id == topology_physical_package_id(i))
-			return;
-	}
-	/* was not found, so add it */
-	cpumask_set_cpu(cpu, &rapl_cpu_mask);
+	/* check if cpu's package is already covered.If not, add it.*/
+	cpumask_and(&tmp, &rapl_cpu_mask, topology_core_cpumask(cpu));
+	if (cpumask_empty(&tmp))
+		cpumask_set_cpu(cpu, &rapl_cpu_mask);
 }
 
 static __init void rapl_hsw_server_quirk(void)
-- 
1.9.1

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