lib/ukschedcoop: Add scheduler statistics

Instrument the cooperative scheduler to provide statistics
via the libuksched stats API.

Add a wrapper for yield() to increment the yield counter from
within libukschedcoop.

Use schedcoop_yield() in place of schedcoop_schedule() in the
idle thread, as the latter would cause num_sched to exceed
num_yield, which would errneously imply a preemption, given
that num_preempt = num_sched - num_yield.

Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Reviewed-by: Cezar Craciunoiu <cezar.craciunoiu@unikraft.io>
Reviewed-by: Florin Postolache <florin.postolache.of@gmail.com>
Reviewed-by: Simon Kuenzer <simon@unikraft.io>
Approved-by: Simon Kuenzer <simon@unikraft.io>
GitHub-Closes: #1477

diff --git a/lib/ukschedcoop/schedcoop.c b/lib/ukschedcoop/schedcoop.c
index 5c18ef6596f51287abdc73eb7c68cbd7d9bf654c..b5a04568960cc0bb1e5c82f45bb4b00417a934cc 100644 (file)
--- a/lib/ukschedcoop/schedcoop.c
+++ b/lib/ukschedcoop/schedcoop.c
@@ -105,6 +105,7 @@ static void schedcoop_schedule(struct uk_sched *s)
                 */
                c->idle_return_time = min_wakeup_time;
                next = &c->idle;
+               uk_sched_stats_idle_count_incr(s);
        }
 
        if (next != prev) {
@@ -117,13 +118,26 @@ static void schedcoop_schedule(struct uk_sched *s)
                uk_thread_clear_queueable(next);
        }
 
+       uk_sched_stats_sched_count_incr(s);
+
        ukplat_lcpu_restore_irqf(flags);
 
        /* Interrupting the switch is equivalent to having the next thread
         * interrupted at the return instruction. And therefore at safe point.
         */
-       if (prev != next)
+       if (prev != next) {
+               if (next != &c->idle) {
+                       UK_ASSERT(prev->sched);
+                       uk_sched_stats_next_count_incr(s);
+               }
                uk_sched_thread_switch(next);
+       }
+}
+
+static void schedcoop_yield(struct uk_sched *s)
+{
+       uk_sched_stats_yield_count_incr(s);
+       schedcoop_schedule(s);
 }
 
 static int schedcoop_thread_add(struct uk_sched *s, struct uk_thread *t)
@@ -191,7 +205,13 @@ static __noreturn void idle_thread_fn(void *argp)
                         * Check if something else can be scheduled now.
                         */
                        ukplat_lcpu_restore_irqf(flags);
-                       schedcoop_schedule(&c->sched);
+
+                       /* Use yield() here instead of schedule(), as the
+                        * latter would cause num_sched to exceed num_yield,
+                        * which would errneously imply a preemption, as
+                        * num_preempt = num_sched - num_yield
+                        */
+                       schedcoop_yield(&c->sched);
 
                        continue;
                }
@@ -212,8 +232,13 @@ static __noreturn void idle_thread_fn(void *argp)
 
                ukplat_lcpu_restore_irqf(flags);
 
-               /* try to schedule a thread that might now be available */
-               schedcoop_schedule(&c->sched);
+               /* Try to schedule a thread that might now be available.
+                * Use yield() here instead of schedule(), as the
+                * latter would cause num_sched to exceed num_yield,
+                * which would errneously imply a preemption, as
+                * num_preempt = num_sched - num_yield
+                */
+               schedcoop_yield(&c->sched);
        }
 }
 
@@ -288,7 +313,7 @@ struct uk_sched *uk_schedcoop_create(struct uk_alloc *a,
 
        uk_sched_init(&c->sched,
                        schedcoop_start,
-                       schedcoop_schedule,
+                       schedcoop_yield,
                        schedcoop_thread_add,
                        schedcoop_thread_remove,
                        schedcoop_thread_blocked,