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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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