Re: [PATCH v2] sched: add a tuning knob to allow changing RR tmeslice

[Clark Williams <williams@redhat.com>]

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On Thu, 24 Jan 2013 17:59:55 +0100
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Clark Williams <williams@redhat.com> wrote:
> 
> > This version stores the user-input value in a separate 
> > location from the jiffies values used by the scheduler, to 
> > prevent a race condition.
> > 
> > Subject: [PATCH v2] sched: add a tuning knob to allow changing 
> > RR timeslice
> 
> looks useful.
> 
> > @@ -2010,7 +2010,7 @@ static void task_tick_rt(struct rq *rq, struct
> > task_struct *p, int queued) if (--p->rt.time_slice)
> >  		return;
> >  
> > -	p->rt.time_slice = RR_TIMESLICE;
> > +	p->rt.time_slice = sched_rr_timeslice;
> >  
> >  	/*
> >  	 * Requeue to the end of queue if we (and all of our
> > ancestors) are the @@ -2041,7 +2041,7 @@ static unsigned int
> > get_rr_interval_rt(struct rq *rq, struct task_struct *task)
> >  	 * Time slice is 0 for SCHED_FIFO tasks
> 
> Patch wont apply due to patch corruption, alas.
> 
> 

Easily fixed. Modified for 3.8-rc4:

commit 0e2d40c5c84d06670f85cc212591f27f69f59c62
Author: Clark Williams <williams@redhat.com>
Date:   Thu Jan 24 13:51:01 2013 -0600

    [kernel] sched: add a tuning knob to allow changing RR timeslice
    
    Add a /proc/sys/kernel scheduler knob named sched_rr_timeslice_ms
    that allows global changing of the SCHED_RR timeslice value. User
    visable value is in milliseconds but is stored as jiffies.  Setting
    to 0 (zero) resets to the default (currently 100ms).
    
    Signed-off-by: Clark Williams <williams@redhat.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6fc8f45..d803690 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2082,6 +2082,11 @@ int sched_rt_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos);
 
+extern int sched_rr_timeslice;
+extern int sched_rr_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
+
 #ifdef CONFIG_SCHED_AUTOGROUP
 extern unsigned int sysctl_sched_autogroup_enabled;
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 257002c..5675074 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7507,6 +7507,24 @@ static int sched_rt_global_constraints(void)
 }
 #endif /* CONFIG_RT_GROUP_SCHED */
 
+int sched_rr_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos)
+{
+	int ret;
+	static DEFINE_MUTEX(mutex);
+
+	mutex_lock(&mutex);
+	ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	/* make sure that internally we keep jiffies */
+	/* also, writing zero resets timeslice to default */
+	if (!ret && write) 
+		sched_rr_timeslice = sched_rr_timeslice <= 0 ? 
+			RR_TIMESLICE : msecs_to_jiffies(sched_rr_timeslice);
+	mutex_unlock(&mutex);
+	return ret;
+}
+
 int sched_rt_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 418feb0..6c54e83 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -11,6 +11,8 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
 
 struct rt_bandwidth def_rt_bandwidth;
 
+int sched_rr_timeslice = RR_TIMESLICE;
+
 static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
 {
 	struct rt_bandwidth *rt_b =
@@ -2010,7 +2012,7 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
 	if (--p->rt.time_slice)
 		return;
 
-	p->rt.time_slice = RR_TIMESLICE;
+	p->rt.time_slice = sched_rr_timeslice;
 
 	/*
 	 * Requeue to the end of queue if we (and all of our ancestors) are the
@@ -2041,7 +2043,7 @@ static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
 	 * Time slice is 0 for SCHED_FIFO tasks
 	 */
 	if (task->policy == SCHED_RR)
-		return RR_TIMESLICE;
+		return sched_rr_timeslice;
 	else
 		return 0;
 }
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c88878d..1eabf86 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -403,6 +403,14 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= sched_rt_handler,
 	},
+	{
+		.procname	= "sched_rr_timeslice_ms",
+		.data		= &sched_rr_timeslice,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= sched_rr_handler,
+	},
+
 #ifdef CONFIG_SCHED_AUTOGROUP
 	{
 		.procname	= "sched_autogroup_enabled",


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