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sched: tidy up SCHED_RR

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- make timeslices of SCHED_RR tasks constant and not
dependent on task's static_prio [1] ;
- remove obsolete code (timeslice related bits);
- make sched_rr_get_interval() return something more
meaningful [2] for SCHED_OTHER tasks.

[1] according to the following link, it's not compliant with SUSv3
(not sure though, what is the reference for us :-)
http://lkml.org/lkml/2007/3/7/656

[2] the interval is dynamic and can be depicted as follows "should a
task be one of the runnable tasks at this particular moment, it would
expect to run for this interval of time before being re-scheduled by the
scheduler tick".
(i.e. it's more precise if a task is runnable at the moment)

yeah, this seems to require task_rq_lock/unlock() but this is not a hot
path.

results:

(SCHED_FIFO)

dimm@earth:~/storage/prog$ sudo chrt -f 10 ./rr_interval 
time_slice: 0 : 0

(SCHED_RR)

dimm@earth:~/storage/prog$ sudo chrt 10 ./rr_interval 
time_slice: 0 : 99984800

(SCHED_NORMAL)

dimm@earth:~/storage/prog$ ./rr_interval 
time_slice: 0 : 19996960

(SCHED_NORMAL + a cpu_hog of similar 'weight' on the same CPU --- so should be a half of the previous result)

dimm@earth:~/storage/prog$ taskset 1 ./rr_interval 
time_slice: 0 : 9998480

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Dmitry Adamushko 2007-10-15 17:00:13 +02:00 committed by Ingo Molnar
parent a9957449b0
commit a4ec24b48d
2 changed files with 18 additions and 25 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

41
kernel/sched.c
View file

@ -96,7 +96,7 @@ unsigned long long __attribute__((weak)) sched_clock(void)
/*
* Some helpers for converting nanosecond timing to jiffy resolution
*/
#define NS_TO_JIFFIES(TIME) ((TIME) / (1000000000 / HZ))
#define NS_TO_JIFFIES(TIME) ((unsigned long)(TIME) / (1000000000 / HZ))
#define JIFFIES_TO_NS(TIME) ((TIME) * (1000000000 / HZ))
#define NICE_0_LOAD SCHED_LOAD_SCALE
@ -105,11 +105,9 @@ unsigned long long __attribute__((weak)) sched_clock(void)
/*
* These are the 'tuning knobs' of the scheduler:
*
* Minimum timeslice is 5 msecs (or 1 jiffy, whichever is larger),
* default timeslice is 100 msecs, maximum timeslice is 800 msecs.
* default timeslice is 100 msecs (used only for SCHED_RR tasks).
* Timeslices get refilled after they expire.
*/
#define MIN_TIMESLICE max(5 * HZ / 1000, 1)
#define DEF_TIMESLICE (100 * HZ / 1000)
#ifdef CONFIG_SMP
@ -133,24 +131,6 @@ static inline void sg_inc_cpu_power(struct sched_group *sg, u32 val)
}
#endif
#define SCALE_PRIO(x, prio) \
max(x * (MAX_PRIO - prio) / (MAX_USER_PRIO / 2), MIN_TIMESLICE)
/*
* static_prio_timeslice() scales user-nice values [ -20 ... 0 ... 19 ]
* to time slice values: [800ms ... 100ms ... 5ms]
*/
static unsigned int static_prio_timeslice(int static_prio)
{
if (static_prio == NICE_TO_PRIO(19))
return 1;
if (static_prio < NICE_TO_PRIO(0))
return SCALE_PRIO(DEF_TIMESLICE * 4, static_prio);
else
return SCALE_PRIO(DEF_TIMESLICE, static_prio);
}
static inline int rt_policy(int policy)
{
if (unlikely(policy == SCHED_FIFO) || unlikely(policy == SCHED_RR))
@ -4746,6 +4726,7 @@ asmlinkage
long sys_sched_rr_get_interval(pid_t pid, struct timespec __user *interval)
{
struct task_struct *p;
unsigned int time_slice;
int retval = -EINVAL;
struct timespec t;
@ -4762,9 +4743,21 @@ long sys_sched_rr_get_interval(pid_t pid, struct timespec __user *interval)
if (retval)
goto out_unlock;
jiffies_to_timespec(p->policy == SCHED_FIFO ?
0 : static_prio_timeslice(p->static_prio), &t);
if (p->policy == SCHED_FIFO)
time_slice = 0;
else if (p->policy == SCHED_RR)
time_slice = DEF_TIMESLICE;
else {
struct sched_entity *se = &p->se;
unsigned long flags;
struct rq *rq;
rq = task_rq_lock(p, &flags);
time_slice = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));
task_rq_unlock(rq, &flags);
}
read_unlock(&tasklist_lock);
jiffies_to_timespec(time_slice, &t);
retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
out_nounlock:
return retval;

2
kernel/sched_rt.c
View file

@ -206,7 +206,7 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p)
if (--p->time_slice)
return;
p->time_slice = static_prio_timeslice(p->static_prio);
p->time_slice = DEF_TIMESLICE;
/*
* Requeue to the end of queue if we are not the only element