[PATCH v2 rcu 1/7] refscale: Add measurement of clock readout

Paul E. McKenney
2021-07-28T17:38:32Z

This commit adds a "clock" type to refscale, which checks the performance
of ktime_get_real_fast_ns(). Use the "clocksource=" kernel boot parameter
to select the underlying clock source.

[ paulmck: Work around compiler false positive per kernel test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index d998a76fb5422..66dc14cf5687e 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -467,6 +467,40 @@ static struct ref_scale_ops acqrel_ops = {
.name = "acqrel"
};

+static volatile u64 stopopts;
+
+static void ref_clock_section(const int nloops)
+{
+ u64 x = 0;
+ int i;
+
+ preempt_disable();
+ for (i = nloops; i >= 0; i--)
+ x += ktime_get_real_fast_ns();
+ preempt_enable();
+ stopopts = x;
+}
+
+static void ref_clock_delay_section(const int nloops, const int udl, const int ndl)
+{
+ u64 x = 0;
+ int i;
+
+ preempt_disable();
+ for (i = nloops; i >= 0; i--) {
+ x += ktime_get_real_fast_ns();
+ un_delay(udl, ndl);
+ }
+ preempt_enable();
+ stopopts = x;
+}
+
+static struct ref_scale_ops clock_ops = {
+ .readsection = ref_clock_section,
+ .delaysection = ref_clock_delay_section,
+ .name = "clock"
+};
+
static void rcu_scale_one_reader(void)
{
if (readdelay <= 0)
@@ -759,7 +793,7 @@ ref_scale_init(void)
int firsterr = 0;
static struct ref_scale_ops *scale_ops[] = {
&rcu_ops, &srcu_ops, &rcu_trace_ops, &rcu_tasks_ops, &refcnt_ops, &rwlock_ops,
- &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops,
+ &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops,
};

if (!torture_init_begin(scale_type, verbose))