[PATCH] Revert "powercap: intel_rapl: Expose all package CPUs in PMU cpumask"

[Dennis Chen <dechen@redhat.com>]

Commit 525e0064f3d8 ("powercap: intel_rapl: Expose all package CPUs in
PMU cpumask") expanded cpumask to include all CPUs in the package.
Since perf opens an event for every CPU in cpumask, the value returned
for power/energy-pkg/ is roughly scaled by the number of CPUs.

On a single-socket 72-core DMR machine the reported value is roughly
72x higher than when perf is restricted to reading from a single CPU:

$ perf stat -e power/energy-pkg/ -- sleep 1
 Performance counter stats for 'system wide':

          8,052.48 Joules power/energy-pkg/

       1.010483558 seconds time elapsed

$ perf stat -C 5 -e power/energy-pkg/ -- sleep 1

 Performance counter stats for 'CPU(s) 5':

            112.15 Joules power/energy-pkg/

       1.009685587 seconds time elapsed

Reverting this commit restores the expected behavior for perf.

Fixes: 525e0064f3d8 ("powercap: intel_rapl: Expose all package CPUs in PMU cpumask")
Cc: stable@vger.kernel.org
Signed-off-by: Dennis Chen <dechen@redhat.com>
---
Changes in v2:
- Simply revert 525e0064f3d8 and don't add associated_cpus sysfs attr

 drivers/powercap/intel_rapl_common.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/powercap/intel_rapl_common.c b/drivers/powercap/intel_rapl_common.c
index 70cab5f08bc6..f58649ff4f53 100644
--- a/drivers/powercap/intel_rapl_common.c
+++ b/drivers/powercap/intel_rapl_common.c
@@ -1139,21 +1139,23 @@ static struct rapl_pmu rapl_pmu;
 
 /* PMU helpers */
 
-static void set_pmu_cpumask(struct rapl_package *rp, cpumask_var_t mask)
+static int get_pmu_cpu(struct rapl_package *rp)
 {
 	int cpu;
 
 	if (!rp->has_pmu)
-		return;
+		return nr_cpu_ids;
 
 	/* Only TPMI & MSR RAPL are supported for now */
 	if (rp->priv->type != RAPL_IF_TPMI && rp->priv->type != RAPL_IF_MSR)
-		return;
+		return nr_cpu_ids;
 
 	/* TPMI/MSR RAPL uses any CPU in the package for PMU */
 	for_each_online_cpu(cpu)
 		if (topology_physical_package_id(cpu) == rp->id)
-			cpumask_set_cpu(cpu, mask);
+			return cpu;
+
+	return nr_cpu_ids;
 }
 
 static bool is_rp_pmu_cpu(struct rapl_package *rp, int cpu)
@@ -1435,6 +1437,7 @@ static ssize_t cpumask_show(struct device *dev,
 {
 	struct rapl_package *rp;
 	cpumask_var_t cpu_mask;
+	int cpu;
 	int ret;
 
 	if (!alloc_cpumask_var(&cpu_mask, GFP_KERNEL))
@@ -1446,7 +1449,9 @@ static ssize_t cpumask_show(struct device *dev,
 
 	/* Choose a cpu for each RAPL Package */
 	list_for_each_entry(rp, &rapl_packages, plist) {
-		set_pmu_cpumask(rp, cpu_mask);
+		cpu = get_pmu_cpu(rp);
+		if (cpu < nr_cpu_ids)
+			cpumask_set_cpu(cpu, cpu_mask);
 	}
 	cpus_read_unlock();
 
-- 
2.56.0