Re: [PATCH 2.6.21] Return available first timeslice to the creator, not parent

[Pavel Emelyanov <xemul@openvz.org>]

Peter Zijlstra wrote:
> On Thu, 2007-08-30 at 09:50 +0200, Vitaly Mayatskikh wrote:
> > Short-living process returns its timeslice to the parent, this affects
> > process that creates a lot of such short-living threads, because its
> > not a parent for new threads. Patch fixes this issue and doesn't break
> > kabi as does the patch from reporter: http://lkml.org/lkml/2007/4/7/21
>
> > plain text document attachment (2.6.21-timeslice.patch), "proposed
> > patch"
> > diff -up -bB ./include/linux/sched.h.orig ./include/linux/sched.h
> > --- ./include/linux/sched.h.orig	2007-08-21 09:20:22.000000000 +0200
> > +++ ./include/linux/sched.h	2007-08-27 10:14:06.000000000 +0200
> > @@ -827,7 +827,9 @@ struct task_struct {
> >  
> >  	unsigned long policy;
> >  	cpumask_t cpus_allowed;
> > -	unsigned int time_slice, first_time_slice;
> > +	unsigned int time_slice;
> > +	/* Pid of creator */
> > +	unsigned int cpid;
>
> might as well make that pid_t, or maybe even a struct pid* and keep a
> reference on it - the struct pid police might have an opinion.

Store the struct pid reference itself. In any case you make
the find_get_pid() later to obtain the struct pid itself. This
will even make the sched_exit() work faster.

> >  #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> >  	struct sched_info sched_info;
> > diff -up -bB ./kernel/sched.c.orig ./kernel/sched.c
> > --- ./kernel/sched.c.orig	2007-08-21 09:20:22.000000000 +0200
> > +++ ./kernel/sched.c	2007-08-27 10:18:44.000000000 +0200
> > @@ -1626,9 +1626,9 @@ void fastcall sched_fork(struct task_str
> >  	p->time_slice = (current->time_slice + 1) >> 1;
> >  	/*
> >  	 * The remainder of the first timeslice might be recovered by
> > -	 * the parent if the child exits early enough.
> > +	 * the creator (not parent!) if the child exits early enough.
> >  	 */
> > -	p->first_time_slice = 1;
> > +	p->cpid = current->pid;
> >  	current->time_slice >>= 1;
> >  	p->timestamp = sched_clock();
> >  	if (unlikely(!current->time_slice)) {
> > @@ -1728,33 +1728,46 @@ void fastcall wake_up_new_task(struct ta
> >  
> >  /*
> >   * Potentially available exiting-child timeslices are
> > - * retrieved here - this way the parent does not get
> > + * retrieved here - this way the creator does not get
> >   * penalized for creating too many threads.
> >   *
> >   * (this cannot be used to 'generate' timeslices
> >   * artificially, because any timeslice recovered here
> > - * was given away by the parent in the first place.)
> > + * was given away by the creator in the first place.)
> >   */
> >  void fastcall sched_exit(struct task_struct *p)
> >  {
> >  	unsigned long flags;
> >  	struct rq *rq;
> > -
> > +	struct task_struct* creator = NULL;
> >  	/*
> >  	 * If the child was a (relative-) CPU hog then decrease
> > -	 * the sleep_avg of the parent as well.
> > +	 * the sleep_avg of the creator as well.
> >  	 */
> > -	rq = task_rq_lock(p->parent, &flags);
> > -	if (p->first_time_slice && task_cpu(p) == task_cpu(p->parent)) {
> > -		p->parent->time_slice += p->time_slice;
> > -		if (unlikely(p->parent->time_slice > task_timeslice(p)))
> > -			p->parent->time_slice = task_timeslice(p);
> > +	if (p->cpid) {
> > +		struct pid *pid = find_get_pid((pid_t)p->cpid);
> > +		if (pid) {
> > +			creator = get_pid_task(pid, PIDTYPE_PID);
> > +			put_pid(pid);
> >  	}
> > -	if (p->sleep_avg < p->parent->sleep_avg)
> > -		p->parent->sleep_avg = p->parent->sleep_avg /
> > +
> > +		if (creator) {
> > +			if (task_cpu(p) == task_cpu(creator)) {
> > +				rq = task_rq_lock(creator, &flags);
> > +
> > +				creator->time_slice += p->time_slice;
> > +				if (unlikely(creator->time_slice > task_timeslice(p)))
> > +					creator->time_slice = task_timeslice(p);
> > +
> > +				if (p->sleep_avg < creator->sleep_avg)
> > +					creator->sleep_avg = creator->sleep_avg /
> >  		(EXIT_WEIGHT + 1) * EXIT_WEIGHT + p->sleep_avg /
> >  		(EXIT_WEIGHT + 1);
> >  	task_rq_unlock(rq, &flags);
> > +			}
> > +			put_task_struct(creator);
> > +		}
> > +	}
> >  }
> >  
> >  /**
> > @@ -3153,7 +3166,7 @@ static void task_running_tick(struct rq 
> >  		 */
> >  		if ((p->policy == SCHED_RR) && !--p->time_slice) {
> >  			p->time_slice = task_timeslice(p);
> > -			p->first_time_slice = 0;
> > +			p->cpid = 0;
> >  			set_tsk_need_resched(p);
> >  
> >  			/* put it at the end of the queue: */
> > @@ -3166,7 +3179,7 @@ static void task_running_tick(struct rq 
> >  		set_tsk_need_resched(p);
> >  		p->prio = effective_prio(p);
> >  		p->time_slice = task_timeslice(p);
> > -		p->first_time_slice = 0;
> > +		p->cpid = 0;
> >  
> >  		if (!rq->expired_timestamp)
> >  			rq->expired_timestamp = jiffies;
>
> Other than that it looks good, pretty much what I suggested :-)

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