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sched/fair: Beef up wake_wide() 

Josef Bacik reported that Facebook sees better performance with their
1:N load (1 dispatch/node, N workers/node) when carrying an old patch
to try very hard to wake to an idle CPU.  While looking at wake_wide(),
I noticed that it doesn't pay attention to the wakeup of a many partner
waker, returning 1 only when waking one of its many partners.

Correct that, letting explicit domain flags override the heuristic.

While at it, adjust task_struct bits, we don't need a 64-bit counter.

Tested-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
[ Tidy things up. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team<Kernel-team@fb.com>
Cc: morten.rasmussen@arm.com
Cc: riel@redhat.com
Link: http://lkml.kernel.org/r/1436888390.7983.49.camel@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mike Galbraith 2015-07-14 17:39:50 +02:00 committed by Ingo Molnar
parent fbd705a0c6
commit 63b0e9edce
2 changed files with 35 additions and 36 deletions
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4
include/linux/sched.h
View File

@ -1359,9 +1359,9 @@ struct task_struct {
#ifdef CONFIG_SMP
struct llist_node wake_entry;
int on_cpu;
struct task_struct *last_wakee;
unsigned long wakee_flips;
unsigned int wakee_flips;
unsigned long wakee_flip_decay_ts;
struct task_struct *last_wakee;
int wake_cpu;
#endif

67
kernel/sched/fair.c
View File

@ -4726,26 +4726,29 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
#endif
/*
* Detect M:N waker/wakee relationships via a switching-frequency heuristic.
* A waker of many should wake a different task than the one last awakened
* at a frequency roughly N times higher than one of its wakees. In order
* to determine whether we should let the load spread vs consolodating to
* shared cache, we look for a minimum 'flip' frequency of llc_size in one
* partner, and a factor of lls_size higher frequency in the other. With
* both conditions met, we can be relatively sure that the relationship is
* non-monogamous, with partner count exceeding socket size. Waker/wakee
* being client/server, worker/dispatcher, interrupt source or whatever is
* irrelevant, spread criteria is apparent partner count exceeds socket size.
*/
static int wake_wide(struct task_struct *p)
{
unsigned int master = current->wakee_flips;
unsigned int slave = p->wakee_flips;
int factor = this_cpu_read(sd_llc_size);
/*
* Yeah, it's the switching-frequency, could means many wakee or
* rapidly switch, use factor here will just help to automatically
* adjust the loose-degree, so bigger node will lead to more pull.
*/
if (p->wakee_flips > factor) {
/*
* wakee is somewhat hot, it needs certain amount of cpu
* resource, so if waker is far more hot, prefer to leave
* it alone.
*/
if (current->wakee_flips > (factor * p->wakee_flips))
return 1;
}
return 0;
if (master < slave)
swap(master, slave);
if (slave < factor || master < slave * factor)
return 0;
return 1;
}
static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
@ -4757,13 +4760,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
unsigned long weight;
int balanced;
/*
* If we wake multiple tasks be careful to not bounce
* ourselves around too much.
*/
if (wake_wide(p))
return 0;
idx = sd->wake_idx;
this_cpu = smp_processor_id();
prev_cpu = task_cpu(p);
@ -5017,17 +5013,17 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
{
struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
int cpu = smp_processor_id();
int new_cpu = cpu;
int new_cpu = prev_cpu;
int want_affine = 0;
int sync = wake_flags & WF_SYNC;
if (sd_flag & SD_BALANCE_WAKE)
want_affine = cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
rcu_read_lock();
for_each_domain(cpu, tmp) {
if (!(tmp->flags & SD_LOAD_BALANCE))
continue;
break;
/*
* If both cpu and prev_cpu are part of this domain,
@ -5041,17 +5037,21 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
if (tmp->flags & sd_flag)
sd = tmp;
else if (!want_affine)
break;
}
if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync))
prev_cpu = cpu;
if (sd_flag & SD_BALANCE_WAKE) {
new_cpu = select_idle_sibling(p, prev_cpu);
goto unlock;
if (affine_sd) {
sd = NULL; /* Prefer wake_affine over balance flags */
if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
new_cpu = cpu;
}
while (sd) {
if (!sd) {
if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
new_cpu = select_idle_sibling(p, new_cpu);
} else while (sd) {
struct sched_group *group;
int weight;
@ -5085,7 +5085,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
}
/* while loop will break here if sd == NULL */
}
unlock:
rcu_read_unlock();
return new_cpu;