Changeset efed95a3 in mainline for kernel/generic/src/proc/thread.c

Timestamp:

2024-01-20T17:09:00Z (4 months ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

master

Children:

3d84734

Parents:

286da52

git-author:

Jiří Zárevúcky <zarevucky.jiri@…> (2024-01-20 16:12:46)

git-committer:

Jiří Zárevúcky <zarevucky.jiri@…> (2024-01-20 17:09:00)

Message:

Make thread→cpu weakly atomic, to avoid need for thread lock

File:

• kernel/generic/src/proc/thread.c (modified) (5 diffs)

kernel/generic/src/proc/thread.c

@@ -198 +198 @@
 {
         irq_spinlock_lock(&thread->lock, true);
-        thread->cpu = cpu;
+        atomic_set_unordered(&thread->cpu, cpu);
         thread->nomigrate++;
         irq_spinlock_unlock(&thread->lock, true);
@@ -263 +263 @@
             ((flags & THREAD_FLAG_UNCOUNTED) == THREAD_FLAG_UNCOUNTED);
         thread->priority = -1;          /* Start in rq[0] */
-        thread->cpu = NULL;
+        atomic_init(&thread->cpu, NULL);
         thread->stolen = false;
         thread->uspace =
@@ -343 +343 @@
         /* Clear cpu->fpu_owner if set to this thread. */
 #ifdef CONFIG_FPU_LAZY
-        if (thread->cpu) {
+        cpu_t *cpu = atomic_get_unordered(&thread->cpu);
+        if (cpu) {
                 /*
                  * We need to lock for this because the old CPU can concurrently try
@@ -349 +350 @@
                  * it to finish. An atomic compare-and-swap wouldn't be enough.
                  */
-                irq_spinlock_lock(&thread->cpu->fpu_lock, false);
-
-                thread_t *owner = atomic_load_explicit(&thread->cpu->fpu_owner,
-                    memory_order_relaxed);
-
-                if (owner == thread) {
-                        atomic_store_explicit(&thread->cpu->fpu_owner, NULL,
-                            memory_order_relaxed);
-                }
-
-                irq_spinlock_unlock(&thread->cpu->fpu_lock, false);
+                irq_spinlock_lock(&cpu->fpu_lock, false);
+
+                if (atomic_get_unordered(&cpu->fpu_owner) == thread)
+                        atomic_set_unordered(&cpu->fpu_owner, NULL);
+
+                irq_spinlock_unlock(&cpu->fpu_lock, false);
         }
 #endif
@@ -707 +703 @@
 
         if (additional) {
-                if (thread->cpu)
-                        printf("%-5u", thread->cpu->id);
+                cpu_t *cpu = atomic_get_unordered(&thread->cpu);
+                if (cpu)
+                        printf("%-5u", cpu->id);
                 else
                         printf("none ");