diff options
| -rw-r--r-- | Documentation/scheduler/sched-domains.txt | 32 | ||||
| -rw-r--r-- | kernel/sched.c | 11 | ||||
| -rw-r--r-- | kernel/sched_fair.c | 5 |
3 files changed, 37 insertions, 11 deletions
diff --git a/Documentation/scheduler/sched-domains.txt b/Documentation/scheduler/sched-domains.txt index 373ceacc367e..b7ee379b651b 100644 --- a/Documentation/scheduler/sched-domains.txt +++ b/Documentation/scheduler/sched-domains.txt @@ -1,8 +1,7 @@ -Each CPU has a "base" scheduling domain (struct sched_domain). These are -accessed via cpu_sched_domain(i) and this_sched_domain() macros. The domain +Each CPU has a "base" scheduling domain (struct sched_domain). The domain hierarchy is built from these base domains via the ->parent pointer. ->parent -MUST be NULL terminated, and domain structures should be per-CPU as they -are locklessly updated. +MUST be NULL terminated, and domain structures should be per-CPU as they are +locklessly updated. Each scheduling domain spans a number of CPUs (stored in the ->span field). A domain's span MUST be a superset of it child's span (this restriction could @@ -26,11 +25,26 @@ is treated as one entity. The load of a group is defined as the sum of the load of each of its member CPUs, and only when the load of a group becomes out of balance are tasks moved between groups. -In kernel/sched.c, rebalance_tick is run periodically on each CPU. This -function takes its CPU's base sched domain and checks to see if has reached -its rebalance interval. If so, then it will run load_balance on that domain. -rebalance_tick then checks the parent sched_domain (if it exists), and the -parent of the parent and so forth. +In kernel/sched.c, trigger_load_balance() is run periodically on each CPU +through scheduler_tick(). It raises a softirq after the next regularly scheduled +rebalancing event for the current runqueue has arrived. The actual load +balancing workhorse, run_rebalance_domains()->rebalance_domains(), is then run +in softirq context (SCHED_SOFTIRQ). + +The latter function takes two arguments: the current CPU and whether it was idle +at the time the scheduler_tick() happened and iterates over all sched domains +our CPU is on, starting from its base domain and going up the ->parent chain. +While doing that, it checks to see if the current domain has exhausted its +rebalance interval. If so, it runs load_balance() on that domain. It then checks +the parent sched_domain (if it exists), and the parent of the parent and so +forth. + +Initially, load_balance() finds the busiest group in the current sched domain. +If it succeeds, it looks for the busiest runqueue of all the CPUs' runqueues in +that group. If it manages to find such a runqueue, it locks both our initial +CPU's runqueue and the newly found busiest one and starts moving tasks from it +to our runqueue. The exact number of tasks amounts to an imbalance previously +computed while iterating over this sched domain's groups. *** Implementing sched domains *** The "base" domain will "span" the first level of the hierarchy. In the case diff --git a/kernel/sched.c b/kernel/sched.c index f592ce6f8616..a8845516ace6 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5011,6 +5011,17 @@ recheck: return -EINVAL; } + /* + * If not changing anything there's no need to proceed further: + */ + if (unlikely(policy == p->policy && (!rt_policy(policy) || + param->sched_priority == p->rt_priority))) { + + __task_rq_unlock(rq); + raw_spin_unlock_irqrestore(&p->pi_lock, flags); + return 0; + } + #ifdef CONFIG_RT_GROUP_SCHED if (user) { /* diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 3f7ec9e27ee1..c7ec5c8e7b44 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -22,6 +22,7 @@ #include <linux/latencytop.h> #include <linux/sched.h> +#include <linux/cpumask.h> /* * Targeted preemption latency for CPU-bound tasks: @@ -3850,8 +3851,8 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle) interval = msecs_to_jiffies(interval); if (unlikely(!interval)) interval = 1; - if (interval > HZ*NR_CPUS/10) - interval = HZ*NR_CPUS/10; + if (interval > HZ*num_online_cpus()/10) + interval = HZ*num_online_cpus()/10; need_serialize = sd->flags & SD_SERIALIZE; |