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Date: Fri, 25 Apr 2014 12:54:14 -0700
From: Jason Low <jason.low2@...com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>, mingo@...nel.org,
linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
alex.shi@...aro.org, efault@....de, vincent.guittot@...aro.org,
morten.rasmussen@....com, aswin@...com, chegu_vinod@...com
Subject: Re: [PATCH 1/3] sched, balancing: Update rq->max_idle_balance_cost
whenever newidle balance is attempted
On Fri, 2014-04-25 at 11:43 +0200, Peter Zijlstra wrote:
> So how about something like this? It tracks the minimal next_balance for
> whatever domains we do visit, or the very bottom domain in the
> insta-bail case (but yeah, Mike's got a point.. we could think of
> removing that).
>
> The thought is that since the higher domains have larger intervals
> anyway, its less likely they will move the timer back often, so skipping
> them is not that big a deal.
>
> I also considered tracking next_busy_balance and using that when
> pulled_task, but I decided against it (after I'd actually written the
> code to do so). We were on the brink of going idle, that's really not
> busy.
Preeti mentioned that sd->balance_interval is changed during load_balance().
Should we also consider updating the interval in rebalance_domains() after
calling load_balance(), and also taking max_load_balance_interval into account
in the updates for next_balance in idle_balance()?
If so, how about the something like the below change which also introduces
get_sd_balance_interval() to obtain the sd's balance interval, and have both
update_next_balance() and rebalance_domains() use that function.
Signed-off-by: Jason Low <jason.low2@...com>
---
kernel/sched/fair.c | 81 ++++++++++++++++++++++++++++++++-------------------
1 files changed, 51 insertions(+), 30 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 43232b8..09c546c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6645,27 +6645,59 @@ out:
return ld_moved;
}
+static inline unsigned long get_sd_balance_interval(struct sched_domain *sd, int busy)
+{
+ unsigned long interval = sd->balance_interval;
+
+ if (busy)
+ interval *= sd->busy_factor;
+
+ /* scale ms to jiffies */
+ interval = msecs_to_jiffies(interval);
+ interval = clamp(interval, 1UL, max_load_balance_interval);
+
+ return interval;
+}
+
+static inline void
+update_next_balance(struct sched_domain *sd, int busy, unsigned long *next_balance)
+{
+ unsigned long interval, next;
+
+ interval = get_sd_balance_interval(sd, busy);
+ next = sd->last_balance + interval;
+
+ if (time_after(*next_balance, next))
+ *next_balance = next;
+}
+
/*
* idle_balance is called by schedule() if this_cpu is about to become
* idle. Attempts to pull tasks from other CPUs.
*/
static int idle_balance(struct rq *this_rq)
{
+ unsigned long next_balance = jiffies + HZ;
+ int this_cpu = this_rq->cpu;
struct sched_domain *sd;
int pulled_task = 0;
- unsigned long next_balance = jiffies + HZ;
u64 curr_cost = 0;
- int this_cpu = this_rq->cpu;
idle_enter_fair(this_rq);
+
/*
* We must set idle_stamp _before_ calling idle_balance(), such that we
* measure the duration of idle_balance() as idle time.
*/
this_rq->idle_stamp = rq_clock(this_rq);
- if (this_rq->avg_idle < sysctl_sched_migration_cost)
+ if (this_rq->avg_idle < sysctl_sched_migration_cost) {
+ rcu_read_lock();
+ sd = rcu_dereference_check_sched_domain(this_rq->sd);
+ update_next_balance(sd, 0, &next_balance);
+ rcu_read_unlock();
goto out;
+ }
/*
* Drop the rq->lock, but keep IRQ/preempt disabled.
@@ -6675,15 +6707,16 @@ static int idle_balance(struct rq *this_rq)
update_blocked_averages(this_cpu);
rcu_read_lock();
for_each_domain(this_cpu, sd) {
- unsigned long interval;
int continue_balancing = 1;
u64 t0, domain_cost;
if (!(sd->flags & SD_LOAD_BALANCE))
continue;
- if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost)
+ if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) {
+ update_next_balance(sd, 0, &next_balance);
break;
+ }
if (sd->flags & SD_BALANCE_NEWIDLE) {
t0 = sched_clock_cpu(this_cpu);
@@ -6700,9 +6733,7 @@ static int idle_balance(struct rq *this_rq)
curr_cost += domain_cost;
}
- interval = msecs_to_jiffies(sd->balance_interval);
- if (time_after(next_balance, sd->last_balance + interval))
- next_balance = sd->last_balance + interval;
+ update_next_balance(sd, 0, &next_balance);
if (pulled_task)
break;
}
@@ -6710,27 +6741,22 @@ static int idle_balance(struct rq *this_rq)
raw_spin_lock(&this_rq->lock);
+ if (curr_cost > this_rq->max_idle_balance_cost)
+ this_rq->max_idle_balance_cost = curr_cost;
+
/*
- * While browsing the domains, we released the rq lock.
- * A task could have be enqueued in the meantime
+ * While browsing the domains, we released the rq lock, a task could
+ * have be enqueued in the meantime. Since we're not going idle,
+ * pretend we pulled a task.
*/
- if (this_rq->cfs.h_nr_running && !pulled_task) {
+ if (this_rq->cfs.h_nr_running && !pulled_task)
pulled_task = 1;
- goto out;
- }
- if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
- /*
- * We are going idle. next_balance may be set based on
- * a busy processor. So reset next_balance.
- */
+out:
+ /* Move the next balance forward */
+ if (time_after(this_rq->next_balance, next_balance))
this_rq->next_balance = next_balance;
- }
-
- if (curr_cost > this_rq->max_idle_balance_cost)
- this_rq->max_idle_balance_cost = curr_cost;
-out:
/* Is there a task of a high priority class? */
if (this_rq->nr_running != this_rq->cfs.h_nr_running)
pulled_task = -1;
@@ -7013,13 +7039,7 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
break;
}
- interval = sd->balance_interval;
- if (idle != CPU_IDLE)
- interval *= sd->busy_factor;
-
- /* scale ms to jiffies */
- interval = msecs_to_jiffies(interval);
- interval = clamp(interval, 1UL, max_load_balance_interval);
+ interval = get_sd_balance_interval(sd, idle != CPU_IDLE);
need_serialize = sd->flags & SD_SERIALIZE;
@@ -7038,6 +7058,7 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
idle = idle_cpu(cpu) ? CPU_IDLE : CPU_NOT_IDLE;
}
sd->last_balance = jiffies;
+ interval = get_sd_balance_interval(sd, idle != CPU_IDLE);
}
if (need_serialize)
spin_unlock(&balancing);
--
1.7.1
--
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