[patch] new-context balancing, 2.6.5-rc3-mm1

Ingo Molnar
2004-03-30T21:02:55Z

[-- Attachment #1: Type: text/plain, Size: 384 bytes --]

i've attached sched-balance-context.patch, which is the current version
of fork()/clone() balancing, against 2.6.5-rc3-mm1.

Changes:

- only balance CLONE_VM threads

- take ->cpus_allowed into account when balancing.

i've checked kernel recompiles and while they didnt hurt from fork()
balancing on an 8-way SMP box, i implemented the thread-only balancing
nevertheless.

Ingo

[-- Attachment #2: sched-balance-context.patch --]
[-- Type: text/plain, Size: 4796 bytes --]

--- linux/include/linux/sched.h.orig
+++ linux/include/linux/sched.h
@@ -715,12 +715,17 @@ extern void do_timer(struct pt_regs *);

extern int FASTCALL(wake_up_state(struct task_struct * tsk, unsigned int state));
extern int FASTCALL(wake_up_process(struct task_struct * tsk));
+extern void FASTCALL(wake_up_forked_process(struct task_struct * tsk));
#ifdef CONFIG_SMP
extern void kick_process(struct task_struct *tsk);
+ extern void FASTCALL(wake_up_forked_thread(struct task_struct * tsk));
#else
static inline void kick_process(struct task_struct *tsk) { }
+ static inline void wake_up_forked_thread(struct task_struct * tsk)
+ {
+ return wake_up_forked_process(tsk);
+ }
#endif
-extern void FASTCALL(wake_up_forked_process(struct task_struct * tsk));
extern void FASTCALL(sched_fork(task_t * p));
extern void FASTCALL(sched_exit(task_t * p));

--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -1139,6 +1137,119 @@ enum idle_type
};

#ifdef CONFIG_SMP
+
+/*
+ * find_idlest_cpu - find the least busy runqueue.
+ */
+static int find_idlest_cpu(int this_cpu, runqueue_t *this_rq, cpumask_t mask)
+{
+ unsigned long load, min_load, this_load;
+ int i, min_cpu;
+ cpumask_t tmp;
+
+ min_cpu = UINT_MAX;
+ min_load = ULONG_MAX;
+
+ cpus_and(tmp, mask, cpu_online_map);
+ for_each_cpu_mask(i, tmp) {
+ load = cpu_load(i);
+
+ if (load < min_load) {
+ min_cpu = i;
+ min_load = load;
+
+ /* break out early on an idle CPU: */
+ if (!min_load)
+ break;
+ }
+ }
+
+ /* add +1 to account for the new task */
+ this_load = cpu_load(this_cpu) + SCHED_LOAD_SCALE;
+
+ /*
+ * Would with the addition of the new task to the
+ * current CPU there be an imbalance between this
+ * CPU and the idlest CPU?
+ */
+ if (min_load*this_rq->sd->imbalance_pct < 100*this_load)
+ return min_cpu;
+
+ return this_cpu;
+}
+
+/*
+ * wake_up_forked_thread - wake up a freshly forked thread.
+ *
+ * This function will do some initial scheduler statistics housekeeping
+ * that must be done for every newly created context, and it also does
+ * runqueue balancing.
+ */
+void fastcall wake_up_forked_thread(task_t * p)
+{
+ unsigned long flags;
+ int this_cpu = get_cpu(), cpu;
+ runqueue_t *this_rq = cpu_rq(this_cpu), *rq;
+
+ /*
+ * Migrate the new context to the least busy CPU,
+ * if that CPU is out of balance.
+ */
+ cpu = find_idlest_cpu(this_cpu, this_rq, p->cpus_allowed);
+
+ local_irq_save(flags);
+lock_again:
+ rq = cpu_rq(cpu);
+ double_rq_lock(this_rq, rq);
+
+ BUG_ON(p->state != TASK_RUNNING);
+
+ /*
+ * We did find_idlest_cpu() unlocked, so in theory
+ * the mask could have changed:
+ */
+ if (!cpu_isset(cpu, p->cpus_allowed)) {
+ cpu = any_online_cpu(p->cpus_allowed);
+ double_rq_unlock(this_rq, rq);
+ goto lock_again;
+ }
+ /*
+ * We decrease the sleep average of forking parents
+ * and children as well, to keep max-interactive tasks
+ * from forking tasks that are max-interactive.
+ */
+ current->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(current) *
+ PARENT_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);
+
+ p->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(p) *
+ CHILD_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);
+
+ p->interactive_credit = 0;
+
+ p->prio = effective_prio(p);
+ set_task_cpu(p, cpu);
+
+ if (cpu == this_cpu) {
+ if (unlikely(!current->array))
+ __activate_task(p, rq);
+ else {
+ p->prio = current->prio;
+ list_add_tail(&p->run_list, &current->run_list);
+ p->array = current->array;
+ p->array->nr_active++;
+ rq->nr_running++;
+ }
+ } else {
+ __activate_task(p, rq);
+ if (TASK_PREEMPTS_CURR(p, rq))
+ resched_task(rq->curr);
+ }
+
+ double_rq_unlock(this_rq, rq);
+ local_irq_restore(flags);
+ put_cpu();
+}
+
/*
* If dest_cpu is allowed for this process, migrate the task to it.
* This is accomplished by forcing the cpu_allowed mask to only
--- linux/kernel/fork.c.orig
+++ linux/kernel/fork.c
@@ -1179,9 +1179,23 @@ long do_fork(unsigned long clone_flags,
set_tsk_thread_flag(p, TIF_SIGPENDING);
}

- if (!(clone_flags & CLONE_STOPPED))
- wake_up_forked_process(p); /* do this last */
- else
+ if (!(clone_flags & CLONE_STOPPED)) {
+ /*
+ * Do the wakeup last. On SMP we treat fork() and
+ * CLONE_VM separately, because fork() has already
+ * created cache footprint on this CPU (due to
+ * copying the pagetables), hence migration would
+ * probably be costy. Threads on the other hand
+ * have less traction to the current CPU, and if
+ * there's an imbalance then the scheduler can
+ * migrate this fresh thread now, before it
+ * accumulates a larger cache footprint:
+ */
+ if (clone_flags & CLONE_VM)
+ wake_up_forked_thread(p);
+ else
+ wake_up_forked_process(p);
+ } else
p->state = TASK_STOPPED;
++total_forks;