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Message-ID: <20160331075951.GG3408@twins.programming.kicks-ass.net>
Date: Thu, 31 Mar 2016 09:59:51 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Steve Muckle <steve.muckle@...aro.org>
Cc: Ingo Molnar <mingo@...hat.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
Vincent Guittot <vincent.guittot@...aro.org>,
Morten Rasmussen <morten.rasmussen@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Juri Lelli <Juri.Lelli@....com>,
Patrick Bellasi <patrick.bellasi@....com>,
Michael Turquette <mturquette@...libre.com>,
Byungchul Park <byungchul.park@....com>
Subject: Re: [RFC PATCH] sched/fair: call cpufreq hook in additional paths
On Thu, Mar 24, 2016 at 03:26:07PM -0700, Steve Muckle wrote:
> Note that this patch depends on the 2 patches I sent several days ago:
> http://thread.gmane.org/gmane.linux.kernel/2181498
Right; I had something similar for a little while..
> Unfortunately this means that in the migration case,
> enqueue_entity_load_avg() will end up calling the cpufreq hook twice -
> once via update_cfs_rq_load_avg() and once via
> attach_entity_load_avg().
Right; this is the point where I gave up when I looked at that.
> This should ideally get filtered out before
> the cpufreq driver is invoked but nevertheless is wasteful. Possible
> alternatives to this are
>
> - moving the cpufreq hook from update_cfs_rq_load_avg() into
> its callers (there are three) and also putting the hook
> in attach_task_cfs_rq and detach_task_cfs_rq, resulting in
> five call sites of the hook in fair.c as opposed to three
Its worse; you get a whole nest of extra logic to determine when to call
what. See below (now arguably its still early so I might have made it
more complex than it needed to be..).
>
> - passing an argument into attach_entity_load_avg() to indicate
> whether calling the cpufreq hook is necessary
>
> Both of these are ugly in their own way but would avoid a runtime
> cost. Opinions welcome.
Lemme see what this would look like while I throw the below into the bit
bucket.
---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2854,23 +2854,23 @@ static inline void cfs_rq_util_change(st
static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
{
struct sched_avg *sa = &cfs_rq->avg;
- int decayed, removed_load = 0, removed_util = 0;
+ int ret = 0;
if (atomic_long_read(&cfs_rq->removed_load_avg)) {
s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
sa->load_avg = max_t(long, sa->load_avg - r, 0);
sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
- removed_load = 1;
+ ret |= 1 << 1;
}
if (atomic_long_read(&cfs_rq->removed_util_avg)) {
long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
sa->util_avg = max_t(long, sa->util_avg - r, 0);
sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0);
- removed_util = 1;
+ ret |= 1 << 2;
}
- decayed = __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
+ decayed |= __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
scale_load_down(cfs_rq->load.weight), cfs_rq->curr != NULL, cfs_rq);
#ifndef CONFIG_64BIT
@@ -2878,10 +2878,7 @@ static inline int update_cfs_rq_load_avg
cfs_rq->load_last_update_time_copy = sa->last_update_time;
#endif
- if (decayed || removed_util)
- cfs_rq_util_change(cfs_rq);
-
- return decayed || removed_load;
+ return ret;
}
/* Update task and its cfs_rq load average */
@@ -2891,6 +2888,7 @@ static inline void update_load_avg(struc
u64 now = cfs_rq_clock_task(cfs_rq);
struct rq *rq = rq_of(cfs_rq);
int cpu = cpu_of(rq);
+ int updated;
/*
* Track task load average for carrying it to new CPU after migrated, and
@@ -2900,9 +2898,14 @@ static inline void update_load_avg(struc
se->on_rq * scale_load_down(se->load.weight),
cfs_rq->curr == se, NULL);
- if (update_cfs_rq_load_avg(now, cfs_rq) && update_tg)
+ updated = update_cfs_rq_load_avg(now, cfs_rq);
+
+ if (updated & 5)
+ cfs_rq_util_change(cfs_rq);
+
+ if (update_tg && (updated & 3))
update_tg_load_avg(cfs_rq, 0);
-}
+
static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
@@ -2953,7 +2956,7 @@ enqueue_entity_load_avg(struct cfs_rq *c
{
struct sched_avg *sa = &se->avg;
u64 now = cfs_rq_clock_task(cfs_rq);
- int migrated, decayed;
+ int migrated, updated;
migrated = !sa->last_update_time;
if (!migrated) {
@@ -2962,16 +2965,18 @@ enqueue_entity_load_avg(struct cfs_rq *c
cfs_rq->curr == se, NULL);
}
- decayed = update_cfs_rq_load_avg(now, cfs_rq);
+ updated = update_cfs_rq_load_avg(now, cfs_rq);
cfs_rq->runnable_load_avg += sa->load_avg;
cfs_rq->runnable_load_sum += sa->load_sum;
- if (migrated)
+ if (migrated) {
attach_entity_load_avg(cfs_rq, se);
-
- if (decayed || migrated)
- update_tg_load_avg(cfs_rq, 0);
+ if (updated & 3)
+ update_tg_load_avg(cfs_rq, 0);
+ } else if (updated & 5) {
+ cfs_rq_util_change(cfs_rq);
+ }
}
/* Remove the runnable load generated by se from cfs_rq's runnable load average */
@@ -6157,6 +6162,7 @@ static void update_blocked_averages(int
struct rq *rq = cpu_rq(cpu);
struct cfs_rq *cfs_rq;
unsigned long flags;
+ int updated;
raw_spin_lock_irqsave(&rq->lock, flags);
update_rq_clock(rq);
@@ -6170,7 +6176,10 @@ static void update_blocked_averages(int
if (throttled_hierarchy(cfs_rq))
continue;
- if (update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq))
+ updated = update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
+ if (updated & 5)
+ cfs_rq_util_change(cfs_rq);
+ if (updated & 3)
update_tg_load_avg(cfs_rq, 0);
}
raw_spin_unlock_irqrestore(&rq->lock, flags);
@@ -6228,10 +6237,13 @@ static inline void update_blocked_averag
struct rq *rq = cpu_rq(cpu);
struct cfs_rq *cfs_rq = &rq->cfs;
unsigned long flags;
+ int updated;
raw_spin_lock_irqsave(&rq->lock, flags);
update_rq_clock(rq);
- update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
+ updated = update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
+ if (updated & 5)
+ cfs_rq_util_change(cfs_rq);
raw_spin_unlock_irqrestore(&rq->lock, flags);
}
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