refscale: Add non-atomic per-CPU increment readers

This commit adds refscale readers based on READ_ONCE() and WRITE_ONCE()
that are unprotected (can lose counts, "refscale.scale_type=incpercpu"),
preempt-disabled ("refscale.scale_type=incpercpupreempt"),
bh-disabled ("refscale.scale_type=incpercpubh"), and irq-disabled
("refscale.scale_type=incpercpuirqsave").  On my x86 laptop, these are
about 4.3ns, 3.8ns, and 7.3ns per pair, respectively.

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 81cb70bad8f802dc1e102297e874c4e6e83d2728..582f730632fcb10eeb2e9f638e50a3e21a107023 100644 (file)
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -382,6 +382,155 @@ static const struct ref_scale_ops percpuinc_ops = {
        .name           = "percpuinc"
 };
 
+// Note that this can lose counts in preemptible kernels.
+static void ref_incpercpu_section(const int nloops)
+{
+       int i;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap = this_cpu_ptr(&test_acqrel);
+
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+       }
+}
+
+static void ref_incpercpu_delay_section(const int nloops, const int udl, const int ndl)
+{
+       int i;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap = this_cpu_ptr(&test_acqrel);
+
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               un_delay(udl, ndl);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+       }
+}
+
+static const struct ref_scale_ops incpercpu_ops = {
+       .init           = rcu_sync_scale_init,
+       .readsection    = ref_incpercpu_section,
+       .delaysection   = ref_incpercpu_delay_section,
+       .name           = "incpercpu"
+};
+
+static void ref_incpercpupreempt_section(const int nloops)
+{
+       int i;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap;
+
+               preempt_disable();
+               tap = this_cpu_ptr(&test_acqrel);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+               preempt_enable();
+       }
+}
+
+static void ref_incpercpupreempt_delay_section(const int nloops, const int udl, const int ndl)
+{
+       int i;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap;
+
+               preempt_disable();
+               tap = this_cpu_ptr(&test_acqrel);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               un_delay(udl, ndl);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+               preempt_enable();
+       }
+}
+
+static const struct ref_scale_ops incpercpupreempt_ops = {
+       .init           = rcu_sync_scale_init,
+       .readsection    = ref_incpercpupreempt_section,
+       .delaysection   = ref_incpercpupreempt_delay_section,
+       .name           = "incpercpupreempt"
+};
+
+static void ref_incpercpubh_section(const int nloops)
+{
+       int i;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap;
+
+               local_bh_disable();
+               tap = this_cpu_ptr(&test_acqrel);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+               local_bh_enable();
+       }
+}
+
+static void ref_incpercpubh_delay_section(const int nloops, const int udl, const int ndl)
+{
+       int i;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap;
+
+               local_bh_disable();
+               tap = this_cpu_ptr(&test_acqrel);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               un_delay(udl, ndl);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+               local_bh_enable();
+       }
+}
+
+static const struct ref_scale_ops incpercpubh_ops = {
+       .init           = rcu_sync_scale_init,
+       .readsection    = ref_incpercpubh_section,
+       .delaysection   = ref_incpercpubh_delay_section,
+       .name           = "incpercpubh"
+};
+
+static void ref_incpercpuirqsave_section(const int nloops)
+{
+       int i;
+       unsigned long flags;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap;
+
+               local_irq_save(flags);
+               tap = this_cpu_ptr(&test_acqrel);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+               local_irq_restore(flags);
+       }
+}
+
+static void ref_incpercpuirqsave_delay_section(const int nloops, const int udl, const int ndl)
+{
+       int i;
+       unsigned long flags;
+
+       for (i = nloops; i >= 0; i--) {
+               unsigned long *tap;
+
+               local_irq_save(flags);
+               tap = this_cpu_ptr(&test_acqrel);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) + 1);
+               un_delay(udl, ndl);
+               WRITE_ONCE(*tap, READ_ONCE(*tap) - 1);
+               local_irq_restore(flags);
+       }
+}
+
+static const struct ref_scale_ops incpercpuirqsave_ops = {
+       .init           = rcu_sync_scale_init,
+       .readsection    = ref_incpercpuirqsave_section,
+       .delaysection   = ref_incpercpuirqsave_delay_section,
+       .name           = "incpercpuirqsave"
+};
+
 // Definitions for rwlock
 static rwlock_t test_rwlock;
 
@@ -1318,8 +1467,10 @@ ref_scale_init(void)
        int firsterr = 0;
        static const struct ref_scale_ops *scale_ops[] = {
                &rcu_ops, &srcu_ops, &srcu_fast_ops, RCU_TRACE_OPS RCU_TASKS_OPS
-               &refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
-               &percpuinc_ops, &acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
+               &refcnt_ops, &percpuinc_ops, &incpercpu_ops, &incpercpupreempt_ops,
+               &incpercpubh_ops, &incpercpuirqsave_ops,
+               &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops,
+               &sched_clock_ops, &clock_ops, &jiffies_ops,
                &preempt_ops, &bh_ops, &irq_ops, &irqsave_ops,
                &typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
        };