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SubjectRe: [PATCH 1/3] sched: enable interrupts and drop rq-lock during newidle balancing
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On Mon, 2008-06-23 at 17:04 -0600, Gregory Haskins wrote:
> We do find_busiest_groups() et. al. without locks held for normal balancing,
> so lets do it for newidle as well. It will allow other cpus to make
> forward progress (against our RQ) while we try to balance and allow
> some interrupts to occur.

Is running f_b_g really that expensive? I was under the impression that
move_tasks() is the expensive one...

> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> ---
>
> kernel/sched.c | 44 ++++++++++++++++++++++++++++++++++++++------
> 1 files changed, 38 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 31f91d9..490e6bc 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3333,6 +3333,16 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd)
> int sd_idle = 0;
> int all_pinned = 0;
> cpumask_t cpus = CPU_MASK_ALL;
> + int nr_running;
> +
> + schedstat_inc(sd, lb_count[CPU_NEWLY_IDLE]);
> +
> + /*
> + * We are in a preempt-disabled section, so dropping the lock/irq
> + * here simply means that other cores may acquire the lock,
> + * and interrupts may occur.
> + */
> + spin_unlock_irq(&this_rq->lock);
>
> /*
> * When power savings policy is enabled for the parent domain, idle
> @@ -3344,7 +3354,6 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd)
> !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
> sd_idle = 1;
>
> - schedstat_inc(sd, lb_count[CPU_NEWLY_IDLE]);
> redo:
> group = find_busiest_group(sd, this_cpu, &imbalance, CPU_NEWLY_IDLE,
> &sd_idle, &cpus, NULL);
> @@ -3366,14 +3375,33 @@ redo:
>
> ld_moved = 0;
> if (busiest->nr_running > 1) {
> - /* Attempt to move tasks */
> - double_lock_balance(this_rq, busiest);
> - /* this_rq->clock is already updated */
> - update_rq_clock(busiest);
> + local_irq_disable();
> + double_rq_lock(this_rq, busiest);
> +
> + BUG_ON(this_cpu != smp_processor_id());
> +
> + /*
> + * Checking rq->nr_running covers both the case where
> + * newidle-balancing pulls a task, as well as if something
> + * else issued a NEEDS_RESCHED (since we would only need
> + * a reschedule if something was moved to us)
> + */
> + if (this_rq->nr_running) {
> + double_rq_unlock(this_rq, busiest);
> + local_irq_enable();
> + goto out_balanced;
> + }
> +
> ld_moved = move_tasks(this_rq, this_cpu, busiest,
> imbalance, sd, CPU_NEWLY_IDLE,
> &all_pinned);
> - spin_unlock(&busiest->lock);
> +
> + nr_running = this_rq->nr_running;
> + double_rq_unlock(this_rq, busiest);
> + local_irq_enable();
> +
> + if (nr_running)
> + goto out_balanced;
>
> if (unlikely(all_pinned)) {
> cpu_clear(cpu_of(busiest), cpus);
> @@ -3382,6 +3410,8 @@ redo:
> }
> }
>
> + spin_lock_irq(&this_rq->lock);
> +
> if (!ld_moved) {
> schedstat_inc(sd, lb_failed[CPU_NEWLY_IDLE]);
> if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
> @@ -3393,6 +3423,8 @@ redo:
> return ld_moved;
>
> out_balanced:
> + spin_lock_irq(&this_rq->lock);
> +
> schedstat_inc(sd, lb_balanced[CPU_NEWLY_IDLE]);
> if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
> !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
>



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