[PATCH v2] sched/cputime: Make IRQ time accounting configurable at boot time

[Bart Van Assche <bvanassche@acm.org>]

IRQ time accounting reduces performance by 40% for some block storage
workloads on Android. Despite this some producers of Android devices
want to keep IRQ time accounting enabled.

Android devices share a single kernel binary across device vendors.
Make IRQ time accounting configurable at boot time such that Android
vendors can decide individually whether or not to enable IRQ time
accounting.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---

Changes between v1 and v2: improved patch description.

 Documentation/admin-guide/kernel-parameters.txt |  4 ++++
 kernel/sched/cputime.c                          | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e5bab29685f..67a2ad3af833 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5611,6 +5611,10 @@
 			non-zero "wait" parameter.  See weight_single
 			and weight_many.
 
+	sched_clock_irqtime= [KNL]
+			Can be used to disable IRQ time accounting if
+			CONFIG_IRQ_TIME_ACCOUNTING=y.
+
 	skew_tick=	[KNL] Offset the periodic timer tick per cpu to mitigate
 			xtime_lock contention on larger systems, and/or RCU lock
 			contention on all systems with CONFIG_MAXSMP set.
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index af7952f12e6c..d9c65017024d 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -24,6 +24,19 @@ DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
 
 static int sched_clock_irqtime;
 
+static int __init sched_clock_irqtime_setup(char *arg)
+{
+	bool enabled;
+
+	if (kstrtobool(arg, &enabled) < 0)
+		pr_err("Invalid sched_clock_irqtime value\n");
+	else
+		sched_clock_irqtime = enabled;
+	return 1;
+}
+
+__setup("sched_clock_irqtime=", sched_clock_irqtime_setup);
+
 void enable_sched_clock_irqtime(void)
 {
 	sched_clock_irqtime = 1;