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Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: sched: Fix rebalance interval calculation sched, doc: Beef up load balancing description sched: Leave sched_setscheduler() earlier if possible, do not disturb SCHED_FIFO tasks
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commit
148086bb64
3 changed files with 37 additions and 11 deletions
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@ -1,8 +1,7 @@
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Each CPU has a "base" scheduling domain (struct sched_domain). These are
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accessed via cpu_sched_domain(i) and this_sched_domain() macros. The domain
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Each CPU has a "base" scheduling domain (struct sched_domain). The domain
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hierarchy is built from these base domains via the ->parent pointer. ->parent
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MUST be NULL terminated, and domain structures should be per-CPU as they
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are locklessly updated.
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MUST be NULL terminated, and domain structures should be per-CPU as they are
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locklessly updated.
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Each scheduling domain spans a number of CPUs (stored in the ->span field).
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A domain's span MUST be a superset of it child's span (this restriction could
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@ -26,11 +25,26 @@ is treated as one entity. The load of a group is defined as the sum of the
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load of each of its member CPUs, and only when the load of a group becomes
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out of balance are tasks moved between groups.
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In kernel/sched.c, rebalance_tick is run periodically on each CPU. This
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function takes its CPU's base sched domain and checks to see if has reached
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its rebalance interval. If so, then it will run load_balance on that domain.
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rebalance_tick then checks the parent sched_domain (if it exists), and the
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parent of the parent and so forth.
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In kernel/sched.c, trigger_load_balance() is run periodically on each CPU
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through scheduler_tick(). It raises a softirq after the next regularly scheduled
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rebalancing event for the current runqueue has arrived. The actual load
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balancing workhorse, run_rebalance_domains()->rebalance_domains(), is then run
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in softirq context (SCHED_SOFTIRQ).
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The latter function takes two arguments: the current CPU and whether it was idle
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at the time the scheduler_tick() happened and iterates over all sched domains
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our CPU is on, starting from its base domain and going up the ->parent chain.
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While doing that, it checks to see if the current domain has exhausted its
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rebalance interval. If so, it runs load_balance() on that domain. It then checks
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the parent sched_domain (if it exists), and the parent of the parent and so
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forth.
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Initially, load_balance() finds the busiest group in the current sched domain.
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If it succeeds, it looks for the busiest runqueue of all the CPUs' runqueues in
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that group. If it manages to find such a runqueue, it locks both our initial
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CPU's runqueue and the newly found busiest one and starts moving tasks from it
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to our runqueue. The exact number of tasks amounts to an imbalance previously
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computed while iterating over this sched domain's groups.
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*** Implementing sched domains ***
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The "base" domain will "span" the first level of the hierarchy. In the case
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@ -5011,6 +5011,17 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
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return -EINVAL;
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}
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/*
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* If not changing anything there's no need to proceed further:
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*/
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if (unlikely(policy == p->policy && (!rt_policy(policy) ||
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param->sched_priority == p->rt_priority))) {
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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return 0;
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}
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#ifdef CONFIG_RT_GROUP_SCHED
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if (user) {
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/*
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@ -22,6 +22,7 @@
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#include <linux/latencytop.h>
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#include <linux/sched.h>
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#include <linux/cpumask.h>
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/*
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* Targeted preemption latency for CPU-bound tasks:
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@ -3850,8 +3851,8 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
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interval = msecs_to_jiffies(interval);
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if (unlikely(!interval))
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interval = 1;
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if (interval > HZ*NR_CPUS/10)
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interval = HZ*NR_CPUS/10;
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if (interval > HZ*num_online_cpus()/10)
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interval = HZ*num_online_cpus()/10;
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need_serialize = sd->flags & SD_SERIALIZE;
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