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Message-ID: <20170321062957.GL11100@X58A-UD3R>
Date: Tue, 21 Mar 2017 15:29:57 +0900
From: Byungchul Park <byungchul.park@....com>
To: <peterz@...radead.org>, <mingo@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <juri.lelli@...il.com>,
<rostedt@...dmis.org>, <kernel-team@....com>
Subject: Re: [PATCH] sched/deadline: Make find_later_rq() choose a closer cpu
in topology
On Tue, Mar 21, 2017 at 10:38:20AM +0900, Byungchul Park wrote:
> When cpudl_find() returns any among free_cpus, the cpu might not be
> closer than others, considering sched domain. For example:
>
> this_cpu: 15
> free_cpus: 0, 1,..., 14 (== later_mask)
> best_cpu: 0
>
> topology:
>
> 0 --+
> +--+
> 1 --+ |
> +-- ... --+
> 2 --+ | |
> +--+ |
> 3 --+ |
>
> ... ...
>
> 12 --+ |
> +--+ |
> 13 --+ | |
> +-- ... -+
> 14 --+ |
> +--+
> 15 --+
>
> In this case, it would be best to select 14 since it's a free cpu and
> closest to 15(this_cpu). However, currently the code select 0(best_cpu)
> even though that's just any among free_cpus. Fix it.
Hello,
I think it would be better to split this into two patches:
1. Clean up cpudl_find() at cpudeadline.c.
2. Make it choose a closer cpu in topology.
I will do it if you agree with my original purpose.
>
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
> kernel/sched/cpudeadline.c | 20 ++++++++------------
> kernel/sched/deadline.c | 29 +++++++++++++++--------------
> 2 files changed, 23 insertions(+), 26 deletions(-)
>
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index fba235c..cb36727 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -119,7 +119,7 @@ static inline int cpudl_maximum(struct cpudl *cp)
> * @p: the task
> * @later_mask: a mask to fill in with the selected CPUs (or NULL)
> *
> - * Returns: int - best CPU (heap maximum if suitable)
> + * Returns: (int)bool - CPUs were found
> */
> int cpudl_find(struct cpudl *cp, struct task_struct *p,
> struct cpumask *later_mask)
> @@ -127,21 +127,17 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
> int best_cpu = -1;
> const struct sched_dl_entity *dl_se = &p->dl;
>
> - if (later_mask &&
> - cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
> - best_cpu = cpumask_any(later_mask);
> - goto out;
> - } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
> - dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
> - best_cpu = cpudl_maximum(cp);
> - if (later_mask)
> + if (later_mask) {
> + if (!cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed) &&
> + cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
> + dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
> + best_cpu = cpudl_maximum(cp);
> cpumask_set_cpu(best_cpu, later_mask);
> + }
> }
>
> -out:
> WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
> -
> - return best_cpu;
> + return best_cpu != -1;
> }
>
> /*
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index a2ce590..45cc3d3 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1324,7 +1324,7 @@ static int find_later_rq(struct task_struct *task)
> struct sched_domain *sd;
> struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
> int this_cpu = smp_processor_id();
> - int best_cpu, cpu = task_cpu(task);
> + int cpu = task_cpu(task);
>
> /* Make sure the mask is initialized first */
> if (unlikely(!later_mask))
> @@ -1337,17 +1337,14 @@ static int find_later_rq(struct task_struct *task)
> * We have to consider system topology and task affinity
> * first, then we can look for a suitable cpu.
> */
> - best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
> - task, later_mask);
> - if (best_cpu == -1)
> + if (!cpudl_find(&task_rq(task)->rd->cpudl, task, later_mask))
> return -1;
>
> /*
> - * If we are here, some target has been found,
> - * the most suitable of which is cached in best_cpu.
> - * This is, among the runqueues where the current tasks
> - * have later deadlines than the task's one, the rq
> - * with the latest possible one.
> + * If we are here, some targets have been found, including
> + * the most suitable which is, among the runqueues where the
> + * current tasks have later deadlines than the task's one, the
> + * rq with the latest possible one.
> *
> * Now we check how well this matches with task's
> * affinity and system topology.
> @@ -1367,6 +1364,7 @@ static int find_later_rq(struct task_struct *task)
> rcu_read_lock();
> for_each_domain(cpu, sd) {
> if (sd->flags & SD_WAKE_AFFINE) {
> + int closest_cpu;
>
> /*
> * If possible, preempting this_cpu is
> @@ -1378,14 +1376,17 @@ static int find_later_rq(struct task_struct *task)
> return this_cpu;
> }
>
> + closest_cpu = cpumask_first_and(later_mask,
> + sched_domain_span(sd));
> /*
> - * Last chance: if best_cpu is valid and is
> - * in the mask, that becomes our choice.
> + * Last chance: if a cpu being in both later_mask
> + * and current sd span is valid, that becomes our
> + * choice. Of course, the latest possible cpu is
> + * already under consideration through later_mask.
> */
> - if (best_cpu < nr_cpu_ids &&
> - cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {
> + if (closest_cpu < nr_cpu_ids) {
> rcu_read_unlock();
> - return best_cpu;
> + return closest_cpu;
> }
> }
> }
> --
> 1.9.1
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