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Subject[PATCH] sched: Rationalize sys_sched_rr_get_interval()
At the moment, static_prio_timeslice() is only used in 
sys_sched_rr_get_interval() and only gives the correct result for
SCHED_FIFO and SCHED_RR tasks as the time slice for normal tasks is
unrelated to the values returned by static_prio_timeslice().

This patch addresses this problem and in the process moves all the code
associated with static_prio_timeslice() to sched_rt.c which is the only
place where it now has relevance.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>

Peter
--
Peter Williams pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce




diff -r 3df82b0661ca include/linux/sched.h
--- a/include/linux/sched.h Mon Sep 03 12:06:59 2007 +1000
+++ b/include/linux/sched.h Mon Sep 03 12:06:59 2007 +1000
@@ -878,6 +878,7 @@ struct sched_class {
void (*set_curr_task) (struct rq *rq);
void (*task_tick) (struct rq *rq, struct task_struct *p);
void (*task_new) (struct rq *rq, struct task_struct *p);
+ unsigned int (*default_timeslice) (struct task_struct *p);
};

struct load_weight {
diff -r 3df82b0661ca kernel/sched.c
--- a/kernel/sched.c Mon Sep 03 12:06:59 2007 +1000
+++ b/kernel/sched.c Mon Sep 03 12:06:59 2007 +1000
@@ -101,16 +101,6 @@ unsigned long long __attribute__((weak))
#define NICE_0_LOAD SCHED_LOAD_SCALE
#define NICE_0_SHIFT SCHED_LOAD_SHIFT

-/*
- * 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.
- * Timeslices get refilled after they expire.
- */
-#define MIN_TIMESLICE max(5 * HZ / 1000, 1)
-#define DEF_TIMESLICE (100 * HZ / 1000)
-
#ifdef CONFIG_SMP
/*
* Divide a load by a sched group cpu_power : (load / sg->__cpu_power)
@@ -131,24 +121,6 @@ static inline void sg_inc_cpu_power(stru
sg->reciprocal_cpu_power = reciprocal_value(sg->__cpu_power);
}
#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)
{
@@ -4784,8 +4756,7 @@ long sys_sched_rr_get_interval(pid_t pid
if (retval)
goto out_unlock;

- jiffies_to_timespec(p->policy == SCHED_FIFO ?
- 0 : static_prio_timeslice(p->static_prio), &t);
+ jiffies_to_timespec(p->sched_class->default_timeslice(p), &t);
read_unlock(&tasklist_lock);
retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
out_nounlock:
diff -r 3df82b0661ca kernel/sched_fair.c
--- a/kernel/sched_fair.c Mon Sep 03 12:06:59 2007 +1000
+++ b/kernel/sched_fair.c Mon Sep 03 12:06:59 2007 +1000
@@ -1159,6 +1159,11 @@ static void set_curr_task_fair(struct rq
}
#endif

+static unsigned int default_timeslice_fair(struct task_struct *p)
+{
+ return NS_TO_JIFFIES(sysctl_sched_min_granularity);
+}
+
/*
* All the scheduling class methods:
*/
@@ -1180,6 +1185,7 @@ struct sched_class fair_sched_class __re
.set_curr_task = set_curr_task_fair,
.task_tick = task_tick_fair,
.task_new = task_new_fair,
+ .default_timeslice = default_timeslice_fair,
};

#ifdef CONFIG_SCHED_DEBUG
diff -r 3df82b0661ca kernel/sched_idletask.c
--- a/kernel/sched_idletask.c Mon Sep 03 12:06:59 2007 +1000
+++ b/kernel/sched_idletask.c Mon Sep 03 12:06:59 2007 +1000
@@ -59,6 +59,11 @@ static void task_tick_idle(struct rq *rq
{
}

+static unsigned int default_timeslice_idle(struct task_struct *p)
+{
+ return 0;
+}
+
/*
* Simple, special scheduling class for the per-CPU idle tasks:
*/
@@ -80,4 +85,5 @@ static struct sched_class idle_sched_cla

.task_tick = task_tick_idle,
/* no .task_new for idle tasks */
+ .default_timeslice = default_timeslice_idle,
};
diff -r 3df82b0661ca kernel/sched_rt.c
--- a/kernel/sched_rt.c Mon Sep 03 12:06:59 2007 +1000
+++ b/kernel/sched_rt.c Mon Sep 03 12:06:59 2007 +1000
@@ -205,6 +205,34 @@ move_one_task_rt(struct rq *this_rq, int
}
#endif

+/*
+ * 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.
+ * Timeslices get refilled after they expire.
+ */
+#define MIN_TIMESLICE max(5 * HZ / 1000, 1)
+#define DEF_TIMESLICE (100 * HZ / 1000)
+
+#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 void task_tick_rt(struct rq *rq, struct task_struct *p)
{
/*
@@ -229,6 +257,14 @@ static void task_tick_rt(struct rq *rq,
}
}

+static unsigned int default_timeslice_rt(struct task_struct *p)
+{
+ if (p->policy == SCHED_FIFO)
+ return 0;
+
+ return static_prio_timeslice(p->static_prio);
+}
+
static struct sched_class rt_sched_class __read_mostly = {
.enqueue_task = enqueue_task_rt,
.dequeue_task = dequeue_task_rt,
@@ -245,4 +281,5 @@ static struct sched_class rt_sched_class
#endif

.task_tick = task_tick_rt,
+ .default_timeslice = default_timeslice_rt,
};
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