refscale: Add preempt_disable() readers

This commit adds refscale readers based on preempt_disable() and
preempt_enable() ("refscale.scale_type=preempt").  On my x86 laptop, these
are about 2.8ns.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 995c189efaf08d8942ff249292d5b08d64b6551c..8f9cd6eff2b5f5a9a39b0394e205ff3526db07bb 100644 (file)
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -629,6 +629,37 @@ static const struct ref_scale_ops jiffies_ops = {
        .name           = "jiffies"
 };
 
+static void ref_preempt_section(const int nloops)
+{
+       int i;
+
+       migrate_disable();
+       for (i = nloops; i >= 0; i--) {
+               preempt_disable();
+               preempt_enable();
+       }
+       migrate_enable();
+}
+
+static void ref_preempt_delay_section(const int nloops, const int udl, const int ndl)
+{
+       int i;
+
+       migrate_disable();
+       for (i = nloops; i >= 0; i--) {
+               preempt_disable();
+               un_delay(udl, ndl);
+               preempt_enable();
+       }
+       migrate_enable();
+}
+
+static const struct ref_scale_ops preempt_ops = {
+       .readsection    = ref_preempt_section,
+       .delaysection   = ref_preempt_delay_section,
+       .name           = "preempt"
+};
+
 static void ref_bh_section(const int nloops)
 {
        int i;
@@ -1261,7 +1292,7 @@ ref_scale_init(void)
                &rcu_ops, &srcu_ops, &srcu_fast_ops, RCU_TRACE_OPS RCU_TASKS_OPS
                &refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
                &acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
-               &bh_ops, &irq_ops, &irqsave_ops,
+               &preempt_ops, &bh_ops, &irq_ops, &irqsave_ops,
                &typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
        };