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    DateThu, 30 Aug 2007 13:48:54 +0400
    FromPavel Emelyanov <>
    SubjectRe: [PATCH 2.6.21] Return available first timeslice to the creator, not parent
    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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