sched/fair: Move se->vruntime normalization state into struct sched_entity

Quoted 7 lines · Mike Galbraith

Quoted 5 lines · Mike Galbraith

Quoted 3 lines · Mike Galbraith

Wakees that were not migrated/normalized eat an unwanted min_vruntime, and likely take a size XXL latency hit. Big box running master bled profusely under heavy load until I turned TTWU_QUEUE off.

Quoted 4 lines

May as well make it official and against master.today. Fly or die little patchlet.

sched/fair: Move se->vruntime normalization state into struct sched_entity

Does this work?

---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 18 +++++++++++-------
 2 files changed, 12 insertions(+), 7 deletions(-)

include/linux/sched.h +1 -0

index 1b43b45a22b9..a2001e01b3df 100644
@@ -1534,6 +1534,7 @@ struct task_struct {
        unsigned sched_reset_on_fork:1;
        unsigned sched_contributes_to_load:1;
        unsigned sched_migrated:1;
+       unsigned sched_remote_wakeup:1;
        unsigned :0; /* force alignment to the next boundary */
 
        /* unserialized, strictly 'current' */

kernel/sched/core.c +10 -6

index 404c0784b1fc..7f2cae4620c7 100644
@@ -1768,13 +1768,15 @@ void sched_ttwu_pending(void)
        cookie = lockdep_pin_lock(&rq->lock);
 
        while (llist) {
+               int wake_flags = 0;
+
                p = llist_entry(llist, struct task_struct, wake_entry);
                llist = llist_next(llist);
-               /*
-                * See ttwu_queue(); we only call ttwu_queue_remote() when
-                * its a x-cpu wakeup.
-                */
-               ttwu_do_activate(rq, p, WF_MIGRATED, cookie);
+
+               if (p->sched_remote_wakeup)
+                       wake_flags = WF_MIGRATED;
+
+               ttwu_do_activate(rq, p, wake_flags, cookie);
        }
 
        lockdep_unpin_lock(&rq->lock, cookie);

@@ -1819,10 +1821,12 @@ void scheduler_ipi(void)
        irq_exit();
 }
 
-static void ttwu_queue_remote(struct task_struct *p, int cpu)
+static void ttwu_queue_remote(struct task_struct *p, int cpu, int
 wake_flags)
 {
        struct rq *rq = cpu_rq(cpu);
 
+       p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
+
        if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
                if (!set_nr_if_polling(rq->idle))

                        smp_send_reschedule(cpu);

kernel/sched/core.c +1 -1

@@ -1869,7 +1873,7 @@ static void ttwu_queue(struct task_struct *p, int
 cpu, int wake_flags)
 #if defined(CONFIG_SMP)
        if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(),
 cpu)) {
                sched_clock_cpu(cpu); /* sync clocks x-cpu */
-               ttwu_queue_remote(p, cpu);
+               ttwu_queue_remote(p, cpu, wake_flags);
                return;

        }

#endif

Quoted 13 lines · Peter Zijlstra

Quoted 11 lines · Mike Galbraith

Quoted 5 lines · Mike Galbraith

Quoted 3 lines · Mike Galbraith

Wakees that were not migrated/normalized eat an unwanted min_vruntime, and likely take a size XXL latency hit. Big box running master bled profusely under heavy load until I turned TTWU_QUEUE off.

May as well make it official and against master.today. Fly or die little patchlet.

sched/fair: Move se->vruntime normalization state into struct sched_entity

Quoted 1 line

Does this work?

This gets rid of the additional lost wakeups introduced during the merge window, thank you!

The pre-existing low-probability lost wakeups still persist, sad to say Can't have everything, I guess.