core_ctl: Add a kernel parameter to disable core_ctl

Add a kernel parameter called "core_ctl_disable_cpumask" to
specify the CPUs for which core_ctl is not needed. As
core_ctl operates on a cluster basis, all of the CPUs in a
given cluster must be specified to disable core_ctl on that
cluster.

Change-Id: Idfdc5b3aa9f54bafe20489e5ded9d96da6eff21c
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>

2 files changed, 48 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 45d680644dfe..7d6fef1aa136 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -750,6 +750,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			seconds. Defaults to 10*60 = 10mins. A value of 0
 			disables the blank timer.
 
+	core_ctl_disable_cpumask= [SMP]
+			Exempt the CPUs from being managed by core_ctl.
+			core_ctl operates on a cluster basis. So all the
+			CPUs in a given cluster must be specified to disable
+			core_ctl for that cluster.
+
 	coredump_filter=
 			[KNL] Change the default value for
 			/proc/<pid>/coredump_filter.
diff --git a/kernel/sched/core_ctl.c b/kernel/sched/core_ctl.c
index 983159cc0646..a904c18704de 100644
--- a/kernel/sched/core_ctl.c
+++ b/kernel/sched/core_ctl.c
@@ -931,6 +931,42 @@ static struct notifier_block __refdata cpu_notifier = {
 
 /* ============================ init code ============================== */
 
+static cpumask_var_t core_ctl_disable_cpumask;
+static bool core_ctl_disable_cpumask_present;
+
+static int __init core_ctl_disable_setup(char *str)
+{
+	if (!*str)
+		return -EINVAL;
+
+	alloc_bootmem_cpumask_var(&core_ctl_disable_cpumask);
+
+	if (cpulist_parse(str, core_ctl_disable_cpumask) < 0) {
+		free_bootmem_cpumask_var(core_ctl_disable_cpumask);
+		return -EINVAL;
+	}
+
+	core_ctl_disable_cpumask_present = true;
+	pr_info("disable_cpumask=%*pbl\n",
+			cpumask_pr_args(core_ctl_disable_cpumask));
+
+	return 0;
+}
+early_param("core_ctl_disable_cpumask", core_ctl_disable_setup);
+
+static bool should_skip(const struct cpumask *mask)
+{
+	if (!core_ctl_disable_cpumask_present)
+		return false;
+
+	/*
+	 * We operate on a cluster basis. Disable the core_ctl for
+	 * a cluster, if all of it's cpus are specified in
+	 * core_ctl_disable_cpumask
+	 */
+	return cpumask_subset(mask, core_ctl_disable_cpumask);
+}
+
 static struct cluster_data *find_cluster_by_first_cpu(unsigned int first_cpu)
 {
 	unsigned int i;
@@ -952,6 +988,9 @@ static int cluster_init(const struct cpumask *mask)
 	unsigned int cpu;
 	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 
+	if (should_skip(mask))
+		return 0;
+
 	if (find_cluster_by_first_cpu(first_cpu))
 		return 0;
 
@@ -1052,6 +1091,9 @@ static int __init core_ctl_init(void)
 {
 	unsigned int cpu;
 
+	if (should_skip(cpu_possible_mask))
+		return 0;
+
 	core_ctl_check_interval = (rq_avg_period_ms - RQ_AVG_TOLERANCE)
 					* NSEC_PER_MSEC;