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Commit 8e77485f authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
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[PATCH] sched-2.5.29-B1 

the attached patch is a comment update of sched.c and it also does a small
cleanup in migration_thread().
parent c5155e55
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Showing with 202 additions and 46 deletions
kernel/sched.c
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......@@ -111,9 +111,9 @@
* BASE_TIMESLICE scales user-nice values [ -20 ... 19 ]
* to time slice values.
*
* The higher a process's priority, the bigger timeslices
* The higher a thread's priority, the bigger timeslices
* it gets during one round of execution. But even the lowest
* priority process gets MIN_TIMESLICE worth of execution time.
* priority thread gets MIN_TIMESLICE worth of execution time.
*
* task_timeslice() is the interface that is used by the scheduler.
*/
......@@ -144,7 +144,7 @@ struct prio_array {
* This is the main, per-CPU runqueue data structure.
*
* Locking rule: those places that want to lock multiple runqueues
* (such as the load balancing or the process migration code), lock
* (such as the load balancing or the thread migration code), lock
* acquire operations must be ordered by ascending &runqueue.
*/
struct runqueue {
......@@ -241,21 +241,24 @@ static inline void enqueue_task(struct task_struct *p, prio_array_t *array)
p->array = array;
}
/*
* effective_prio - return the priority that is based on the static
* priority but is modified by bonuses/penalties.
*
* We scale the actual sleep average [0 .... MAX_SLEEP_AVG]
* into the -5 ... 0 ... +5 bonus/penalty range.
*
* We use 25% of the full 0...39 priority range so that:
*
* 1) nice +19 interactive tasks do not preempt nice 0 CPU hogs.
* 2) nice -20 CPU hogs do not get preempted by nice 0 tasks.
*
* Both properties are important to certain workloads.
*/
static inline int effective_prio(task_t *p)
{
int bonus, prio;
/*
* Here we scale the actual sleep average [0 .... MAX_SLEEP_AVG]
* into the -5 ... 0 ... +5 bonus/penalty range.
*
* We use 25% of the full 0...39 priority range so that:
*
* 1) nice +19 interactive tasks do not preempt nice 0 CPU hogs.
* 2) nice -20 CPU hogs do not get preempted by nice 0 tasks.
*
* Both properties are important to certain workloads.
*/
bonus = MAX_USER_PRIO*PRIO_BONUS_RATIO*p->sleep_avg/MAX_SLEEP_AVG/100 -
MAX_USER_PRIO*PRIO_BONUS_RATIO/100/2;
......@@ -267,6 +270,12 @@ static inline int effective_prio(task_t *p)
return prio;
}
/*
* activate_task - move a task to the runqueue.
* Also update all the scheduling statistics stuff. (sleep average
* calculation, priority modifiers, etc.)
*/
static inline void activate_task(task_t *p, runqueue_t *rq)
{
unsigned long sleep_time = jiffies - p->sleep_timestamp;
......@@ -289,6 +298,9 @@ static inline void activate_task(task_t *p, runqueue_t *rq)
rq->nr_running++;
}
/*
* deactivate_task - remove a task from the runqueue.
*/
static inline void deactivate_task(struct task_struct *p, runqueue_t *rq)
{
rq->nr_running--;
......@@ -298,6 +310,13 @@ static inline void deactivate_task(struct task_struct *p, runqueue_t *rq)
p->array = NULL;
}
/*
* resched_task - mark a task 'to be rescheduled now'.
*
* On UP this means the setting of the need_resched flag, on SMP it
* might also involve a cross-CPU call to trigger the scheduler on
* the target CPU.
*/
static inline void resched_task(task_t *p)
{
#ifdef CONFIG_SMP
......@@ -320,8 +339,10 @@ static inline void resched_task(task_t *p)
#ifdef CONFIG_SMP
/*
* Wait for a process to unschedule. This is used by the exit() and
* ptrace() code.
* wait_task_inactive - wait for a thread to unschedule.
*
* The caller must ensure that the task *will* unschedule sometime soon,
* else this function might spin for a *long* time.
*/
void wait_task_inactive(task_t * p)
{
......@@ -353,9 +374,10 @@ void wait_task_inactive(task_t * p)
#endif
/*
* Kick the remote CPU if the task is running currently,
* this code is used by the signal code to signal tasks
* which are in user-mode as quickly as possible.
* kick_if_running - kick the remote CPU if the task is running currently.
*
* This code is used by the signal code to signal tasks
* which are in user-mode, as quickly as possible.
*
* (Note that we do this lockless - if the task does anything
* while the message is in flight then it will notice the
......@@ -367,13 +389,16 @@ void kick_if_running(task_t * p)
resched_task(p);
}
/*
* Wake up a process. Put it on the run-queue if it's not
* already there. The "current" process is always on the
* run-queue (except when the actual re-schedule is in
* progress), and as such you're allowed to do the simpler
* "current->state = TASK_RUNNING" to mark yourself runnable
* without the overhead of this.
/***
* try_to_wake_up - wake up a thread
* @p: the to-be-woken-up thread
* @sync: do a synchronous wakeup?
*
* Put it on the run-queue if it's not already there. The "current"
* thread is always on the run-queue (except when the actual
* re-schedule is in progress), and as such you're allowed to do
* the simpler "current->state = TASK_RUNNING" to mark yourself
* runnable without the overhead of this.
*
* returns failure only if the task is already active.
*/
......@@ -419,6 +444,12 @@ int wake_up_process(task_t * p)
return try_to_wake_up(p, 0);
}
/*
* wake_up_forked_process - wake up a freshly forked process.
*
* This function will do some initial scheduler statistics housekeeping
* that must be done for every newly created process.
*/
void wake_up_forked_process(task_t * p)
{
runqueue_t *rq = this_rq_lock();
......@@ -443,7 +474,7 @@ void wake_up_forked_process(task_t * p)
/*
* Potentially available exiting-child timeslices are
* retrieved here - this way the parent does not get
* penalized for creating too many processes.
* penalized for creating too many threads.
*
* (this cannot be used to 'generate' timeslices
* artificially, because any timeslice recovered here
......@@ -467,6 +498,10 @@ void sched_exit(task_t * p)
p->sleep_avg) / (EXIT_WEIGHT + 1);
}
/**
* schedule_tail - first thing a freshly forked thread must call.
* @prev: the thread we just switched away from.
*/
#if CONFIG_SMP || CONFIG_PREEMPT
asmlinkage void schedule_tail(task_t *prev)
{
......@@ -474,6 +509,10 @@ asmlinkage void schedule_tail(task_t *prev)
}
#endif
/*
* context_switch - switch to the new MM and the new
* thread's register state.
*/
static inline task_t * context_switch(task_t *prev, task_t *next)
{
struct mm_struct *mm = next->mm;
......@@ -497,6 +536,13 @@ static inline task_t * context_switch(task_t *prev, task_t *next)
return prev;
}
/*
* nr_running, nr_uninterruptible and nr_context_switches:
*
* externally visible scheduler statistics: current number of runnable
* threads, current number of uninterruptible-sleeping threads, total
* number of context switches performed since bootup.
*/
unsigned long nr_running(void)
{
unsigned long i, sum = 0;
......@@ -564,8 +610,10 @@ static inline void double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2)
#if CONFIG_SMP
/*
* Lock the busiest runqueue as well, this_rq is locked already.
* Recalculate nr_running if we have to drop the runqueue lock.
* double_lock_balance - lock the busiest runqueue
*
* this_rq is locked already. Recalculate nr_running if we have to
* drop the runqueue lock.
*/
static inline unsigned int double_lock_balance(runqueue_t *this_rq,
runqueue_t *busiest, int this_cpu, int idle, unsigned int nr_running)
......@@ -586,6 +634,9 @@ static inline unsigned int double_lock_balance(runqueue_t *this_rq,
return nr_running;
}
/*
* find_busiest_queue - find the busiest runqueue.
*/
static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu, int idle, int *imbalance)
{
int nr_running, load, max_load, i;
......@@ -662,7 +713,7 @@ static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu,
}
/*
* Move a task from a remote runqueue to the local runqueue.
* pull_task - move a task from a remote runqueue to the local runqueue.
* Both runqueues must be locked.
*/
static inline void pull_task(runqueue_t *src_rq, prio_array_t *src_array, task_t *p, runqueue_t *this_rq, int this_cpu)
......@@ -766,8 +817,8 @@ static void load_balance(runqueue_t *this_rq, int idle)
}
/*
* One of the idle_cpu_tick() or the busy_cpu_tick() function will
* gets called every timer tick, on every CPU. Our balancing action
* One of the idle_cpu_tick() and busy_cpu_tick() functions will
* get called every timer tick, on every CPU. Our balancing action
* frequency and balancing agressivity depends on whether the CPU is
* idle or not.
*
......@@ -852,7 +903,7 @@ void scheduler_tick(int user_ticks, int sys_ticks)
/*
* The task was running during this tick - update the
* time slice counter and the sleep average. Note: we
* do not update a process's priority until it either
* do not update a thread's priority until it either
* goes to sleep or uses up its timeslice. This makes
* it possible for interactive tasks to use up their
* timeslices at their highest priority levels.
......@@ -884,7 +935,7 @@ void scheduler_tick(int user_ticks, int sys_ticks)
void scheduling_functions_start_here(void) { }
/*
* 'schedule()' is the main scheduler function.
* schedule() is the main scheduler function.
*/
asmlinkage void schedule(void)
{
......@@ -1038,6 +1089,12 @@ static void __wake_up_common(wait_queue_head_t *q, unsigned int mode, int nr_exc
}
}
/**
* __wake_up - wake up threads blocked on a waitqueue.
* @q: the waitqueue
* @mode: which threads
* @nr_exclusive: how many wake-one or wake-many threads to wake up
*/
void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
unsigned long flags;
......@@ -1060,6 +1117,17 @@ void __wake_up_locked(wait_queue_head_t *q, unsigned int mode)
#if CONFIG_SMP
/**
* __wake_up - sync- wake up threads blocked on a waitqueue.
* @q: the waitqueue
* @mode: which threads
* @nr_exclusive: how many wake-one or wake-many threads to wake up
*
* The sync wakeup differs that the waker knows that it will schedule
* away soon, so while the target thread will be woken up, it will not
* be migrated to another CPU - ie. the two threads are 'synchronized'
* with each other. This can prevent needless bouncing between CPUs.
*/
void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
unsigned long flags;
......@@ -1211,11 +1279,12 @@ void set_user_nice(task_t *p, long nice)
#ifndef __alpha__
/*
* This has been replaced by sys_setpriority. Maybe it should be
* moved into the arch dependent tree for those ports that require
* it for backward compatibility?
* sys_nice - change the priority of the current process.
* @increment: priority increment
*
* sys_setpriority is a more generic, but much slower function that
* does similar things.
*/
asmlinkage long sys_nice(int increment)
{
int retval;
......@@ -1251,9 +1320,11 @@ asmlinkage long sys_nice(int increment)
#endif
/*
* This is the priority value as seen by users in /proc
/**
* task_prio - return the priority value of a given task.
* @p: the task in question.
*
* This is the priority value as seen by users in /proc.
* RT tasks are offset by -200. Normal tasks are centered
* around 0, value goes from -16 to +15.
*/
......@@ -1262,21 +1333,36 @@ int task_prio(task_t *p)
return p->prio - MAX_USER_RT_PRIO;
}
/**
* task_nice - return the nice value of a given task.
* @p: the task in question.
*/
int task_nice(task_t *p)
{
return TASK_NICE(p);
}
/**
* idle_cpu - is a given cpu idle currently?
* @cpu: the processor in question.
*/
int idle_cpu(int cpu)
{
return cpu_curr(cpu) == cpu_rq(cpu)->idle;
}
/**
* find_process_by_pid - find a process with a matching PID value.
* @pid: the pid in question.
*/
static inline task_t *find_process_by_pid(pid_t pid)
{
return pid ? find_task_by_pid(pid) : current;
}
/*
* setscheduler - change the scheduling policy and/or RT priority of a thread.
*/
static int setscheduler(pid_t pid, int policy, struct sched_param *param)
{
struct sched_param lp;
......@@ -1363,17 +1449,32 @@ static int setscheduler(pid_t pid, int policy, struct sched_param *param)
return retval;
}
/**
* sys_sched_setscheduler - set/change the scheduler policy and RT priority
* @pid: the pid in question.
* @policy: new policy
* @param: structure containing the new RT priority.
*/
asmlinkage long sys_sched_setscheduler(pid_t pid, int policy,
struct sched_param *param)
{
return setscheduler(pid, policy, param);
}
/**
* sys_sched_setparam - set/change the RT priority of a thread
* @pid: the pid in question.
* @param: structure containing the new RT priority.
*/
asmlinkage long sys_sched_setparam(pid_t pid, struct sched_param *param)
{
return setscheduler(pid, -1, param);
}
/**
* sys_sched_getscheduler - get the policy (scheduling class) of a thread
* @pid: the pid in question.
*/
asmlinkage long sys_sched_getscheduler(pid_t pid)
{
int retval = -EINVAL;
......@@ -1396,6 +1497,11 @@ asmlinkage long sys_sched_getscheduler(pid_t pid)
return retval;
}
/**
* sys_sched_getscheduler - get the RT priority of a thread
* @pid: the pid in question.
* @param: structure containing the RT priority.
*/
asmlinkage long sys_sched_getparam(pid_t pid, struct sched_param *param)
{
struct sched_param lp;
......@@ -1520,6 +1626,13 @@ asmlinkage int sys_sched_getaffinity(pid_t pid, unsigned int len,
return real_len;
}
/**
* sys_sched_yield - yield the current processor to other threads.
*
* this function yields the current CPU by moving the calling thread
* to the expired array. If there are no other threads running on this
* CPU then this function will return.
*/
asmlinkage long sys_sched_yield(void)
{
runqueue_t *rq = this_rq_lock();
......@@ -1557,12 +1670,25 @@ void __cond_resched(void)
schedule();
}
/**
* yield - yield the current processor to other threads.
*
* this is a shortcut for kernel-space yielding - it marks the
* thread runnable and calls sys_sched_yield().
*/
void yield(void)
{
set_current_state(TASK_RUNNING);
sys_sched_yield();
}
/**
* sys_sched_get_priority_max - return maximum RT priority.
* @policy: scheduling class.
*
* this syscall returns the maximum rt_priority that can be used
* by a given scheduling class.
*/
asmlinkage long sys_sched_get_priority_max(int policy)
{
int ret = -EINVAL;
......@@ -1579,6 +1705,13 @@ asmlinkage long sys_sched_get_priority_max(int policy)
return ret;
}
/**
* sys_sched_get_priority_mix - return minimum RT priority.
* @policy: scheduling class.
*
* this syscall returns the minimum rt_priority that can be used
* by a given scheduling class.
*/
asmlinkage long sys_sched_get_priority_min(int policy)
{
int ret = -EINVAL;
......@@ -1594,6 +1727,14 @@ asmlinkage long sys_sched_get_priority_min(int policy)
return ret;
}
/**
* sys_sched_rr_get_interval - return the default timeslice of a process.
* @pid: pid of the process.
* @interval: userspace pointer to the timeslice value.
*
* this syscall writes the default timeslice value of a given process
* into the user-space timespec buffer. A value of '0' means infinity.
*/
asmlinkage long sys_sched_rr_get_interval(pid_t pid, struct timespec *interval)
{
int retval = -EINVAL;
......@@ -1769,7 +1910,7 @@ typedef struct {
} migration_req_t;
/*
* Change a given task's CPU affinity. Migrate the process to a
* Change a given task's CPU affinity. Migrate the thread to a
* proper CPU and schedule it away if the CPU it's executing on
* is removed from the allowed bitmask.
*
......@@ -1794,7 +1935,7 @@ void set_cpus_allowed(task_t *p, unsigned long new_mask)
p->cpus_allowed = new_mask;
/*
* Can the task run on the task's current CPU? If not then
* migrate the process off to a proper CPU.
* migrate the thread off to a proper CPU.
*/
if (new_mask & (1UL << task_cpu(p))) {
task_rq_unlock(rq, &flags);
......@@ -1843,11 +1984,15 @@ static int migration_startup_thread(void * data)
return 0;
}
static int migration_thread(void * bind_cpu)
/*
* migration_thread - this is a highprio system thread that performs
* thread migration by 'pulling' threads into the target runqueue.
*/
static int migration_thread(void * data)
{
int cpu = (int) (long) bind_cpu;
struct sched_param param = { sched_priority: MAX_RT_PRIO-1 };
migration_startup_t startup;
int cpu = (long) data;
runqueue_t *rq;
int ret, pid;
......@@ -1859,6 +2004,13 @@ static int migration_thread(void * bind_cpu)
startup.thread = current;
pid = kernel_thread(migration_startup_thread, &startup,
CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
/*
* Migration can happen without a migration thread on the
* target CPU because here we remove the thread from the
* runqueue and the helper thread then moves this thread
* to the target CPU - we'll wake up there.
*/
down(&migration_startup);
/* we need to waitpid() to release the helper thread */
......@@ -1868,7 +2020,7 @@ static int migration_thread(void * bind_cpu)
* At this point the startup helper thread must have
* migrated us to the proper CPU already:
*/
if (smp_processor_id() != (int)bind_cpu)
if (smp_processor_id() != cpu)
BUG();
printk("migration_task %d on cpu=%d\n", cpu, smp_processor_id());
......@@ -1927,6 +2079,10 @@ static int migration_thread(void * bind_cpu)
}
}
/*
* migration_call - callback that gets triggered when a CPU is added.
* Here we can start up the necessary migration thread for the new CPU.
*/
static int migration_call(struct notifier_block *nfb,
unsigned long action,
void *hcpu)
......@@ -1989,7 +2145,7 @@ void __init sched_init(void)
}
/*
* We have to do a little magic to get the first
* process right in SMP mode.
* thread right in SMP mode.
*/
rq = this_rq();
rq->curr = current;
......
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