From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Josef Bacik <jbacik@fb.com>,
riel@redhat.com, mingo@redhat.com, linux-kernel@vger.kernel.org,
morten.rasmussen@arm.com, kernel-team <Kernel-team@fb.com>
Subject: Re: [patch] sched: beef up wake_wide()
Date: Tue, 14 Jul 2015 17:04:55 +0200 [thread overview]
Message-ID: <20150714150455.GM19282@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1436883466.7983.17.camel@gmail.com>
On Tue, Jul 14, 2015 at 04:17:46PM +0200, Mike Galbraith wrote:
> There's a buglet,
> We'll not look for a idle cpu when wake_wide() naks want_affine.
*sigh* indeed.. fixing that'll bring us very close to what we started
out wiht..
The one XXX there raises the question on whether we should always so
select_idle_sibling() if we do not have a suitable balance flag, or only
on wakeups.
---
Subject: sched: Beef up wake_wide()
From: Mike Galbraith <umgwanakikbuti@gmail.com>
Date: Fri, 10 Jul 2015 07:19:26 +0200
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 64bit counter.
Cc: morten.rasmussen@arm.com
Cc: riel@redhat.com
Cc: mingo@redhat.com
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Tested-by: Josef Bacik <jbacik@fb.com>
[peterz: frobbings]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1436505566.5715.50.camel@gmail.com
---
include/linux/sched.h | 4 +-
kernel/sched/fair.c | 69 ++++++++++++++++++++++++--------------------------
2 files changed, 36 insertions(+), 37 deletions(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4726,26 +4726,29 @@ static long effective_load(struct task_g
#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_doma
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);
@@ -5015,19 +5011,19 @@ static int get_cpu_usage(int cpu)
static int
select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
{
- struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
+ 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 *
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_flags & 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 *
}
/* while loop will break here if sd == NULL */
}
-unlock:
rcu_read_unlock();
return new_cpu;
next prev parent reply other threads:[~2015-07-14 15:05 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-27 21:22 [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE Josef Bacik
2015-05-28 3:46 ` Mike Galbraith
2015-05-28 9:49 ` Morten Rasmussen
2015-05-28 10:57 ` Mike Galbraith
2015-05-28 11:48 ` Morten Rasmussen
2015-05-28 11:49 ` Mike Galbraith
2015-05-28 10:21 ` Peter Zijlstra
2015-05-28 11:05 ` Peter Zijlstra
2015-05-28 14:27 ` Josef Bacik
2015-05-29 21:03 ` Josef Bacik
2015-05-30 3:55 ` Mike Galbraith
2015-06-01 19:38 ` Josef Bacik
2015-06-01 20:42 ` Peter Zijlstra
2015-06-01 21:03 ` Josef Bacik
2015-06-02 17:12 ` Josef Bacik
2015-06-03 14:12 ` Rik van Riel
2015-06-03 14:24 ` Peter Zijlstra
2015-06-03 14:49 ` Josef Bacik
2015-06-03 15:30 ` Mike Galbraith
2015-06-03 15:57 ` Josef Bacik
2015-06-03 16:53 ` Mike Galbraith
2015-06-03 17:16 ` Josef Bacik
2015-06-03 17:43 ` Mike Galbraith
2015-06-03 20:34 ` Josef Bacik
2015-06-04 4:52 ` Mike Galbraith
2015-06-01 22:15 ` Rik van Riel
2015-06-11 20:33 ` Josef Bacik
2015-06-12 3:42 ` Rik van Riel
2015-06-12 5:35 ` Mike Galbraith
2015-06-17 18:06 ` Josef Bacik
2015-06-18 0:55 ` Mike Galbraith
2015-06-18 3:46 ` Josef Bacik
2015-06-18 4:12 ` Mike Galbraith
2015-07-02 17:44 ` Josef Bacik
2015-07-03 6:40 ` Mike Galbraith
2015-07-03 9:29 ` Mike Galbraith
2015-07-04 15:57 ` Mike Galbraith
2015-07-05 7:17 ` Mike Galbraith
2015-07-06 5:13 ` Mike Galbraith
2015-07-06 14:34 ` Josef Bacik
2015-07-06 18:36 ` Mike Galbraith
2015-07-06 19:41 ` Josef Bacik
2015-07-07 4:01 ` Mike Galbraith
2015-07-07 9:43 ` [patch] " Mike Galbraith
2015-07-07 13:40 ` Josef Bacik
2015-07-07 15:24 ` Mike Galbraith
2015-07-07 17:06 ` Josef Bacik
2015-07-08 6:13 ` [patch] sched: beef up wake_wide() Mike Galbraith
2015-07-09 13:26 ` Peter Zijlstra
2015-07-09 14:07 ` Mike Galbraith
2015-07-09 14:46 ` Mike Galbraith
2015-07-10 5:19 ` Mike Galbraith
2015-07-10 13:41 ` Josef Bacik
2015-07-10 20:59 ` Josef Bacik
2015-07-11 3:11 ` Mike Galbraith
2015-07-13 13:53 ` Josef Bacik
2015-07-14 11:19 ` Peter Zijlstra
2015-07-14 13:49 ` Mike Galbraith
2015-07-14 14:07 ` Peter Zijlstra
2015-07-14 14:17 ` Mike Galbraith
2015-07-14 15:04 ` Peter Zijlstra [this message]
2015-07-14 15:39 ` Mike Galbraith
2015-07-14 16:01 ` Josef Bacik
2015-07-14 17:59 ` Mike Galbraith
2015-07-15 17:11 ` Josef Bacik
2015-08-03 17:07 ` [tip:sched/core] sched/fair: Beef " tip-bot for Mike Galbraith
2015-05-28 11:16 ` [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE Mike Galbraith
2015-05-28 11:49 ` Ingo Molnar
2015-05-28 12:15 ` Mike Galbraith
2015-05-28 12:19 ` Peter Zijlstra
2015-05-28 12:29 ` Ingo Molnar
2015-05-28 15:22 ` David Ahern
2015-05-28 11:55 ` Srikar Dronamraju
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