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Message-ID: <54020F00.2030807@linux.vnet.ibm.com>
Date: Sat, 30 Aug 2014 23:20:56 +0530
From: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To: Vincent Guittot <vincent.guittot@...aro.org>, peterz@...radead.org,
mingo@...nel.org, linux-kernel@...r.kernel.org,
linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org
CC: riel@...hat.com, Morten.Rasmussen@....com, efault@....de,
nicolas.pitre@...aro.org, linaro-kernel@...ts.linaro.org,
daniel.lezcano@...aro.org, dietmar.eggemann@....com
Subject: Re: [PATCH v5 08/12] sched: move cfs task on a CPU with higher capacity
Hi Vincent,
On 08/26/2014 04:36 PM, Vincent Guittot wrote:
> If the CPU is used for handling lot of IRQs, trig a load balance to check if
> it's worth moving its tasks on another CPU that has more capacity.
>
> As a sidenote, this will note generate more spurious ilb because we already
> trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that
> has a task, we will trig the ilb once for migrating the task.
>
> The nohz_kick_needed function has been cleaned up a bit while adding the new
> test
>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> kernel/sched/fair.c | 69 +++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 49 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 18db43e..60ae1ce 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6049,6 +6049,14 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> return true;
> }
>
> + /*
> + * The group capacity is reduced probably because of activity from other
> + * sched class or interrupts which use part of the available capacity
> + */
> + if ((sg->sgc->capacity_orig * 100) > (sgs->group_capacity *
> + env->sd->imbalance_pct))
Wouldn't the check on avg_load let us know if we are packing more tasks
in this group than its capacity ? Isn't that the metric we are more
interested in?
> + return true;
> +
> return false;
> }
>
> @@ -6534,13 +6542,23 @@ static int need_active_balance(struct lb_env *env)
> struct sched_domain *sd = env->sd;
>
> if (env->idle == CPU_NEWLY_IDLE) {
> + int src_cpu = env->src_cpu;
>
> /*
> * ASYM_PACKING needs to force migrate tasks from busy but
> * higher numbered CPUs in order to pack all tasks in the
> * lowest numbered CPUs.
> */
> - if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu)
> + if ((sd->flags & SD_ASYM_PACKING) && src_cpu > env->dst_cpu)
> + return 1;
> +
> + /*
> + * If the CPUs share their cache and the src_cpu's capacity is
> + * reduced because of other sched_class or IRQs, we trig an
> + * active balance to move the task
> + */
> + if ((capacity_orig_of(src_cpu) * 100) > (capacity_of(src_cpu) *
> + sd->imbalance_pct))
> return 1;
> }
>
> @@ -6643,6 +6661,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
>
> schedstat_add(sd, lb_imbalance[idle], env.imbalance);
>
> + env.src_cpu = busiest->cpu;
> +
> ld_moved = 0;
> if (busiest->nr_running > 1) {
> /*
> @@ -6652,7 +6672,6 @@ static int load_balance(int this_cpu, struct rq *this_rq,
> * correctly treated as an imbalance.
> */
> env.flags |= LBF_ALL_PINNED;
> - env.src_cpu = busiest->cpu;
> env.src_rq = busiest;
> env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running);
>
> @@ -7359,10 +7378,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
>
> /*
> * Current heuristic for kicking the idle load balancer in the presence
> - * of an idle cpu is the system.
> + * of an idle cpu in the system.
> * - This rq has more than one task.
> - * - At any scheduler domain level, this cpu's scheduler group has multiple
> - * busy cpu's exceeding the group's capacity.
> + * - This rq has at least one CFS task and the capacity of the CPU is
> + * significantly reduced because of RT tasks or IRQs.
> + * - At parent of LLC scheduler domain level, this cpu's scheduler group has
> + * multiple busy cpu.
> * - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
> * domain span are idle.
> */
> @@ -7372,9 +7393,10 @@ static inline int nohz_kick_needed(struct rq *rq)
> struct sched_domain *sd;
> struct sched_group_capacity *sgc;
> int nr_busy, cpu = rq->cpu;
> + bool kick = false;
>
> if (unlikely(rq->idle_balance))
> - return 0;
> + return false;
>
> /*
> * We may be recently in ticked or tickless idle mode. At the first
> @@ -7388,38 +7410,45 @@ static inline int nohz_kick_needed(struct rq *rq)
> * balancing.
> */
> if (likely(!atomic_read(&nohz.nr_cpus)))
> - return 0;
> + return false;
>
> if (time_before(now, nohz.next_balance))
> - return 0;
> + return false;
>
> if (rq->nr_running >= 2)
Will this check ^^ not catch those cases which this patch is targeting?
Regards
Preeti U Murthy
> - goto need_kick;
> + return true;
>
> rcu_read_lock();
> sd = rcu_dereference(per_cpu(sd_busy, cpu));
> -
> if (sd) {
> sgc = sd->groups->sgc;
> nr_busy = atomic_read(&sgc->nr_busy_cpus);
>
> - if (nr_busy > 1)
> - goto need_kick_unlock;
> + if (nr_busy > 1) {
> + kick = true;
> + goto unlock;
> + }
> +
> }
>
> - sd = rcu_dereference(per_cpu(sd_asym, cpu));
> + sd = rcu_dereference(rq->sd);
> + if (sd) {
> + if ((rq->cfs.h_nr_running >= 1) &&
> + ((rq->cpu_capacity * sd->imbalance_pct) <
> + (rq->cpu_capacity_orig * 100))) {
> + kick = true;
> + goto unlock;
> + }
> + }
>
> + sd = rcu_dereference(per_cpu(sd_asym, cpu));
> if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
> sched_domain_span(sd)) < cpu))
> - goto need_kick_unlock;
> + kick = true;
>
> +unlock:
> rcu_read_unlock();
> - return 0;
> -
> -need_kick_unlock:
> - rcu_read_unlock();
> -need_kick:
> - return 1;
> + return kick;
> }
> #else
> static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
>
--
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