sched: tidy up SCHED_RR
- 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>
diff --git a/kernel/sched.c b/kernel/sched.c
index ce9bb7a..f370f10 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -96,7 +96,7 @@
/*
* 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 @@
/*
* 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 @@
}
#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 @@
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 @@
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;
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 2f26c3d..d0097a0 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -206,7 +206,7 @@
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
