Changeset ec8ef12 in mainline for kernel/generic/src/proc/scheduler.c

Timestamp:

2023-04-19T09:31:02Z (20 months ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

master, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

c0757e1f

Parents:

117ad5a2

Message:

Split find_best_thread() into two functions

try_find_thread() attempts to get a thread from runqueues and returns
NULL when there's none available. find_best_thread() functions as
before and goes to sleep between attempts to find a thread to run.

The purpose of this split is that we can use the non-sleeping version
in the context of a previously running thread to avoid an additional
context switch in case new thread is immediately available.

File:

• kernel/generic/src/proc/scheduler.c (modified) (2 diffs)

kernel/generic/src/proc/scheduler.c

@@ -178 +178 @@
  *
  */
-static thread_t *find_best_thread(int *rq_index)
-{
+static thread_t *try_find_thread(int *rq_index)
+{
+        assert(interrupts_disabled());
         assert(CPU != NULL);
 
-loop:
-        if (atomic_load(&CPU->nrdy) == 0) {
-                /*
-                 * For there was nothing to run, the CPU goes to sleep
-                 * until a hardware interrupt or an IPI comes.
-                 * This improves energy saving and hyperthreading.
-                 */
-                CPU->idle = true;
-
-                /*
-                 * Go to sleep with interrupts enabled.
-                 * Ideally, this should be atomic, but this is not guaranteed on
-                 * all platforms yet, so it is possible we will go sleep when
-                 * a thread has just become available.
-                 */
-                cpu_interruptible_sleep();
-
-                /* Interrupts are disabled again. */
-                goto loop;
-        }
-
-        assert(!CPU->idle);
-
-        unsigned int i;
-        for (i = 0; i < RQ_COUNT; i++) {
+        if (atomic_load(&CPU->nrdy) == 0)
+                return NULL;
+
+        for (int i = 0; i < RQ_COUNT; i++) {
                 irq_spinlock_lock(&(CPU->rq[i].lock), false);
                 if (CPU->rq[i].n == 0) {
@@ -249 +229 @@
         }
 
-        goto loop;
+        return NULL;
+}
+
+/** Get thread to be scheduled
+ *
+ * Get the optimal thread to be scheduled
+ * according to thread accounting and scheduler
+ * policy.
+ *
+ * @return Thread to be scheduled.
+ *
+ */
+static thread_t *find_best_thread(int *rq_index)
+{
+        assert(interrupts_disabled());
+        assert(CPU != NULL);
+
+        while (true) {
+                thread_t *thread = try_find_thread(rq_index);
+
+                if (thread != NULL)
+                        return thread;
+
+                /*
+                 * For there was nothing to run, the CPU goes to sleep
+                 * until a hardware interrupt or an IPI comes.
+                 * This improves energy saving and hyperthreading.
+                 */
+                CPU->idle = true;
+
+                /*
+                 * Go to sleep with interrupts enabled.
+                 * Ideally, this should be atomic, but this is not guaranteed on
+                 * all platforms yet, so it is possible we will go sleep when
+                 * a thread has just become available.
+                 */
+                cpu_interruptible_sleep();
+        }
 }