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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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