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Date: Sun, 27 Apr 2014 14:01:45 +0530
From: Preeti Murthy <preeti.lkml@...il.com>
To: Jason Low <jason.low2@...com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Alex Shi <alex.shi@...aro.org>, Mike Galbraith <efault@....de>,
Vincent Guittot <vincent.guittot@...aro.org>,
Morten Rasmussen <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
Hi Jason, Peter,
The below patch looks good to me except for one point.
In idle_balance() the below code snippet does not look right:
- 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;
- }
By not checking this_rq->next_balance against jiffies,
we might end up not updating this parameter when it
has expired.
So shouldn't it be:
if (time_after(jiffies, this_rq->next_balance) ||
time_after(this_rq->next_balance, next_balance))
this_rq->next_balance = next_balance;
Besides this:
Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Regards
Preeti U Murthy
On Sat, Apr 26, 2014 at 1:24 AM, Jason Low <jason.low2@...com> wrote:
> 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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