refscale: Add measurement of clock readout

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 d998a76..66dc14c 100644 (file)
--- 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))