From 637f50851b57a32f7ec67c50fc16f1601ab1a87a Mon Sep 17 00:00:00 2001 From: Gregory Haskins Date: Fri, 25 Jan 2008 21:08:18 +0100 Subject: [PATCH] sched: only balance our RT tasks within our domain We move the rt-overload data as the first global to per-domain reclassification. This limits the scope of overload related cache-line bouncing to stay with a specified partition instead of affecting all cpus in the system. Finally, we limit the scope of find_lowest_cpu searches to the domain instead of the entire system. Note that we would always respect domain boundaries even without this patch, but we first would scan potentially all cpus before whittling the list down. Now we can avoid looking at RQs that are out of scope, again reducing cache-line hits. Note: In some cases, task->cpus_allowed will effectively reduce our search to within our domain. However, I believe there are cases where the cpus_allowed mask may be all ones and therefore we err on the side of caution. If it can be optimized later, so be it. Signed-off-by: Gregory Haskins CC: Christoph Lameter Signed-off-by: Ingo Molnar --- kernel/sched.c | 7 ++++++ kernel/sched_rt.c | 57 ++++++++++++++++++++++++++--------------------- 2 files changed, 38 insertions(+), 26 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 34b7d721d735..35ef06c99214 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -365,6 +365,13 @@ struct root_domain { atomic_t refcount; cpumask_t span; cpumask_t online; + + /* + * The "RT overload" flag: it gets set if a CPU has more than + * one runnable RT task. + */ + cpumask_t rto_mask; + atomic_t rto_count; }; static struct root_domain def_root_domain; diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index 4d0a60e47dfa..b049e5110eea 100644 --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -5,22 +5,14 @@ #ifdef CONFIG_SMP -/* - * The "RT overload" flag: it gets set if a CPU has more than - * one runnable RT task. - */ -static cpumask_t rt_overload_mask; -static atomic_t rto_count; - -static inline int rt_overloaded(void) +static inline int rt_overloaded(struct rq *rq) { - return atomic_read(&rto_count); + return atomic_read(&rq->rd->rto_count); } static inline void rt_set_overload(struct rq *rq) { - rq->rt.overloaded = 1; - cpu_set(rq->cpu, rt_overload_mask); + cpu_set(rq->cpu, rq->rd->rto_mask); /* * Make sure the mask is visible before we set * the overload count. That is checked to determine @@ -29,23 +21,25 @@ static inline void rt_set_overload(struct rq *rq) * updated yet. */ wmb(); - atomic_inc(&rto_count); + atomic_inc(&rq->rd->rto_count); } static inline void rt_clear_overload(struct rq *rq) { /* the order here really doesn't matter */ - atomic_dec(&rto_count); - cpu_clear(rq->cpu, rt_overload_mask); - rq->rt.overloaded = 0; + atomic_dec(&rq->rd->rto_count); + cpu_clear(rq->cpu, rq->rd->rto_mask); } static void update_rt_migration(struct rq *rq) { - if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1)) + if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1)) { rt_set_overload(rq); - else + rq->rt.overloaded = 1; + } else { rt_clear_overload(rq); + rq->rt.overloaded = 0; + } } #endif /* CONFIG_SMP */ @@ -306,7 +300,7 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask) int count = 0; int cpu; - cpus_and(*lowest_mask, cpu_online_map, task->cpus_allowed); + cpus_and(*lowest_mask, task_rq(task)->rd->online, task->cpus_allowed); /* * Scan each rq for the lowest prio. @@ -580,18 +574,12 @@ static int pull_rt_task(struct rq *this_rq) struct task_struct *p, *next; struct rq *src_rq; - /* - * If cpusets are used, and we have overlapping - * run queue cpusets, then this algorithm may not catch all. - * This is just the price you pay on trying to keep - * dirtying caches down on large SMP machines. - */ - if (likely(!rt_overloaded())) + if (likely(!rt_overloaded(this_rq))) return 0; next = pick_next_task_rt(this_rq); - for_each_cpu_mask(cpu, rt_overload_mask) { + for_each_cpu_mask(cpu, this_rq->rd->rto_mask) { if (this_cpu == cpu) continue; @@ -811,6 +799,20 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p) } } +/* Assumes rq->lock is held */ +static void join_domain_rt(struct rq *rq) +{ + if (rq->rt.overloaded) + rt_set_overload(rq); +} + +/* Assumes rq->lock is held */ +static void leave_domain_rt(struct rq *rq) +{ + if (rq->rt.overloaded) + rt_clear_overload(rq); +} + static void set_curr_task_rt(struct rq *rq) { struct task_struct *p = rq->curr; @@ -840,4 +842,7 @@ const struct sched_class rt_sched_class = { .set_curr_task = set_curr_task_rt, .task_tick = task_tick_rt, + + .join_domain = join_domain_rt, + .leave_domain = leave_domain_rt, }; -- GitLab