kpriv/linux-hardened
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

sched: Fix the rq->next_balance logic in rebalance_domains() and idle_balance()

Browse source 
Currently, in idle_balance(), we update rq->next_balance when we pull_tasks.
However, it is also important to update this in the !pulled_tasks case too.

When the CPU is "busy" (the CPU isn't idle), rq->next_balance gets computed
using sd->busy_factor (so we increase the balance interval when the CPU is
busy). However, when the CPU goes idle, rq->next_balance could still be set
to a large value that was computed with the sd->busy_factor.

Thus, we need to also update rq->next_balance in idle_balance() in the cases
where !pulled_tasks too, so that rq->next_balance gets updated without taking
the busy_factor into account when the CPU is about to go idle.

This patch makes rq->next_balance get updated independently of whether or
not we pulled_task. Also, we add logic to ensure that we always traverse
at least 1 of the sched domains to get a proper next_balance value for
updating rq->next_balance.

Additionally, since load_balance() modifies the sd->balance_interval, we
need to re-obtain the sched domain's interval after the call to
load_balance() in rebalance_domains() before we update rq->next_balance.

This patch adds and uses 2 new helper functions, update_next_balance() and
get_sd_balance_interval() to update next_balance and obtain the sched
domain's balance_interval.

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: daniel.lezcano@linaro.org
Cc: alex.shi@linaro.org
Cc: efault@gmx.de
Cc: vincent.guittot@linaro.org
Cc: morten.rasmussen@arm.com
Cc: aswin@hp.com
Link: http://lkml.kernel.org/r/1399596562.2200.7.camel@j-VirtualBox
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Jason Low 2014-05-08 17:49:22 -07:00 committed by Ingo Molnar
parent a9467fa3cd
commit 52a08ef1f1
1 changed files with 47 additions and 24 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

71
kernel/sched/fair.c
View file

@ -6672,17 +6672,44 @@ out:
return ld_moved;
}
static inline unsigned long
get_sd_balance_interval(struct sched_domain *sd, int cpu_busy)
{
unsigned long interval = sd->balance_interval;
if (cpu_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 cpu_busy, unsigned long *next_balance)
{
unsigned long interval, next;
interval = get_sd_balance_interval(sd, cpu_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);
@ -6692,8 +6719,15 @@ static int idle_balance(struct rq *this_rq)
*/
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);
if (sd)
update_next_balance(sd, 0, &next_balance);
rcu_read_unlock();
goto out;
}
/*
* Drop the rq->lock, but keep IRQ/preempt disabled.
@ -6703,15 +6737,16 @@ 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);
@ -6727,9 +6762,7 @@ 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);
/*
* Stop searching for tasks to pull if there are
@ -6753,15 +6786,11 @@ static int idle_balance(struct rq *this_rq)
if (this_rq->cfs.h_nr_running && !pulled_task)
pulled_task = 1;
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.
*/
this_rq->next_balance = next_balance;
}
out:
/* Move the next balance forward */
if (time_after(this_rq->next_balance, next_balance))
this_rq->next_balance = next_balance;
/* Is there a task of a high priority class? */
if (this_rq->nr_running != this_rq->cfs.h_nr_running)
pulled_task = -1;
@ -7044,16 +7073,9 @@ 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;
if (need_serialize) {
if (!spin_trylock(&balancing))
goto out;
@ -7069,6 +7091,7 @@ 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);