On Mon, 7 Aug 2017 12:50:33 +0900 Byungchul Park <[email protected]> wrote:
> It would be better to avoid pushing tasks to other cpu within > a SD_PREFER_SIBLING domain, instead, get more chances to check other > siblings. > > Signed-off-by: Byungchul Park <[email protected]> > --- > kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 43 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 0223694..2fd1591 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1319,12 +1319,35 @@ static struct task_struct > *pick_earliest_pushable_dl_task(struct rq *rq, int cpu > > static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl); > > +/* > + * Find the first cpu in: mask & sd & ~prefer > + */ > +static int find_cpu(const struct cpumask *mask, > + const struct sched_domain *sd, > + const struct sched_domain *prefer) > +{ > + const struct cpumask *sds = sched_domain_span(sd); > + const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL; > + int cpu = -1; > + > + while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) { > + if (!cpumask_test_cpu(cpu, sds)) > + continue; > + if (ps && cpumask_test_cpu(cpu, ps)) > + continue; > + break; > + } > + > + return cpu; > +} > + > static int find_later_rq(struct task_struct *task) > { > - struct sched_domain *sd; > + struct sched_domain *sd, *prefer = NULL; > struct cpumask *later_mask = > this_cpu_cpumask_var_ptr(local_cpu_mask_dl); > int this_cpu = smp_processor_id(); > int cpu = task_cpu(task); > + int fallback_cpu = -1; > > /* Make sure the mask is initialized first */ > if (unlikely(!later_mask)) > @@ -1376,8 +1399,7 @@ static int find_later_rq(struct task_struct *task) > return this_cpu; > } > > - best_cpu = cpumask_first_and(later_mask, > - sched_domain_span(sd)); > + best_cpu = find_cpu(later_mask, sd, prefer); > /* > * Last chance: if a cpu being in both later_mask > * and current sd span is valid, that becomes our > @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task) > * already under consideration through later_mask. > */ > if (best_cpu < nr_cpu_ids) { > + /* > + * If current domain is SD_PREFER_SIBLING > + * flaged, we have to get more chances to > + * check other siblings. > + */ > + if (sd->flags & SD_PREFER_SIBLING) { > + prefer = sd; Is this how the SD_PREFER_SIBLING works? According to this, the preferred sd is the next sd in for_each_domain(). Not to mention, the prefer variable stays set if the next domain has no available CPUs. Is that what we want? -- Steve > + if (fallback_cpu == -1) > + fallback_cpu = best_cpu; > + continue; > + } > rcu_read_unlock(); > return best_cpu; > } > @@ -1393,6 +1426,13 @@ static int find_later_rq(struct task_struct *task) > rcu_read_unlock(); > > /* > + * If fallback_cpu is valid, all our guesses failed *except* for > + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu. > + */ > + if (fallback_cpu != -1) > + return fallback_cpu; > + > + /* > * At this point, all our guesses failed, we just return > * 'something', and let the caller sort the things out. > */
