Re: scheduler interactivity - does this patch help?

[Con Kolivas <kernel@kolivas.org>]

On Tue, 10 Jun 2003 05:22, Felipe Alfaro Solana wrote:
> On Mon, 2003-06-09 at 07:43, Martin J. Bligh wrote:
> > I've had this patch (I think from Ingo) kicking around in -mjb
> > for a while. I'm going to drop it unless someone thinks it's useful
> > for some testcase you have ... anyone interested?
> >
> > Thanks,
> >
> > M.
> >
> > diff -urpN -X /home/fletch/.diff.exclude 400-reiserfs_dio/kernel/sched.c
> > 420-sched_interactive/kernel/sched.c ---
> > 400-reiserfs_dio/kernel/sched.c	Fri May 30 19:26:34 2003
> > +++ 420-sched_interactive/kernel/sched.c	Fri May 30 19:28:06 2003
> > @@ -89,6 +89,8 @@ int node_threshold = 125;
> >  #define STARVATION_LIMIT	(starvation_limit)
> >  #define NODE_THRESHOLD		(node_threshold)
> >
> > +#define TIMESLICE_GRANULARITY (HZ/20 ?: 1)
> > +
> >  /*
> >   * If a task is 'interactive' then we reinsert it in the active
> >   * array after it has expired its current timeslice. (it will not
> > @@ -1365,6 +1367,27 @@ void scheduler_tick(int user_ticks, int
> >  			enqueue_task(p, rq->expired);
> >  		} else
> >  			enqueue_task(p, rq->active);
> > +	} else {
> > +		/*
> > +		 * Prevent a too long timeslice allowing a task to monopolize
> > +		 * the CPU. We do this by splitting up the timeslice into
> > +		 * smaller pieces.
> > +		 *
> > +		 * Note: this does not mean the task's timeslices expire or
> > +		 * get lost in any way, they just might be preempted by
> > +		 * another task of equal priority. (one with higher
> > +		 * priority would have preempted this task already.) We
> > +		 * requeue this task to the end of the list on this priority
> > +		 * level, which is in essence a round-robin of tasks with
> > +		 * equal priority.
> > +		 */
> > +		if (!(p->time_slice % TIMESLICE_GRANULARITY) &&
> > +			       		(p->array == rq->active)) {
> > +			dequeue_task(p, rq->active);
> > +			set_tsk_need_resched(p);
> > +			p->prio = effective_prio(p);
> > +			enqueue_task(p, rq->active);
> > +		}
> >  	}
> >  out_unlock:
> >  	spin_unlock(&rq->lock);
>
> I'm currently testing it on a modified 2.5.70-mm6 kernel (with HZ set to
> 1000) and seems to help a little with XMMS's chunky audio playback when
> X is reniced to -20.

I tried this patch way back when mingo first posted it and found it helped a 
little. Have a close look at it, though; all it does is limit max timeslice 
to 50ms when other tasks are running at the same priority. A better effect 
can and is obtained by changing max_timeslice to 50ms...

Con