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

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

[Vitaly Mayatskikh]

[-- Attachment #1: Type: text/plain, Size: 3650 bytes --]


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

An example and script for systemtap were modified a bit. Patch was tested on 2.6.21 with results:

Pass 1: parsed user script and 54 library script(s) in 330usr/10sys/340real ms.
Pass 2: analyzed script: 3 probe(s), 10 function(s), 0 embed(s), 10 global(s) in 540usr/890sys/1445real ms.
Pass 3: translated to C into "/tmp/stapg9EJ30/stap_09f64923e2e59e40ae9680eee1ee0ac9_7206.c" in 10usr/0sys/5real ms.
Pass 4: compiled C into "stap_09f64923e2e59e40ae9680eee1ee0ac9_7206.ko" in 2880usr/250sys/3124real ms.
Pass 5: starting run.
sched_exit/enter:  pid = 16625, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16625, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16626, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16626, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16627, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16627, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16628, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16628, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16629, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16629, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16637, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16637, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16638, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16638, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16639, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16639, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16640, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16640, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16641, tgid = 16623, ppid = 3761, creator = 16624, avail. timeslice = 6, creator's timeslice = 5
sched_exit/return: pid = 16641, tgid = 16623, ppid = 3761, creator = 16624, creator's adjusted timeslice = 11
sched_exit/enter:  pid = 16624, tgid = 16623, ppid = 3761, creator = 16623, avail. timeslice = 11, creator's timeslice = 10
sched_exit/return: pid = 16624, tgid = 16623, ppid = 3761, creator = 16623, creator's adjusted timeslice = 21
sched_exit/enter:  pid = 16623, tgid = 16623, ppid = 3761, creator = 3761, avail. timeslice = 21, creator's timeslice = 21
sched_exit/return: pid = 16623, tgid = 16623, ppid = 3761, creator = 3761, creator's adjusted timeslice = 42
Pass 5: run completed in 40usr/150sys/4266real ms.


[-- Attachment #2: proposed patch --]
[-- Type: text/plain, Size: 3490 bytes --]

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;
 
 #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;

[-- Attachment #3: test app sources --]
[-- Type: text/plain, Size: 1174 bytes --]

///////////////////////////////////////////////////////////////////////////////
/// satthread.c ///////////////////////////////////////////////////////////////
/*
 * satthread - Create child thread and join it several times. Each child thread
 *             does nothing and exits immediately.
 *
 * Copyright (C) 2007 Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

#define NTHREAD 10

static void *thread_fn(void *arg)
{
	return NULL;
}

static void *creator(void* arg)
{
	int i;
	pthread_t t;
	for (i = 0; i < NTHREAD; i++) {
		if (pthread_create(&t, NULL, thread_fn, NULL)) {
			fprintf(stderr, "pthread_create(%d) failed\n", i);
			exit(EXIT_FAILURE);
		}
		usleep(100 * 1000);
		pthread_join(t, NULL);
	}
}

int
main(int argc, char **argv)
{
	int i;
	pthread_t t;
	if (pthread_create(&t, NULL, creator, NULL)) {
		fprintf(stderr, "pthread_create (creator) failed\n");
		exit(EXIT_FAILURE);
	}
	pthread_join(t, NULL);
	exit(EXIT_SUCCESS);
}

[-- Attachment #4.1: test script for stap --]
[-- Type: text/plain, Size: 1633 bytes --]

///////////////////////////////////////////////////////////////////////////////
/// fork_exit.stp /////////////////////////////////////////////////////////////
/*
 * fork_exit.stp - Overlooks sched_fork()/exit_exit() for satprocess/satthread
 *                 and prints some information
 *
 * Copyright (C) 2007 Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
 * Copyright (C) 2007 Vitaly Mayatskikh <vmayatsk@redhat.com>
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 */
 
function is_my_testpro(comm)
{
	if (comm == "satthread" || comm == "satprocess" || comm == "thread-stress")
		return 1
	else
		return 0
}

function get_creators_timeslice:long(cpid:long)
%{
    struct task_struct* creator = 0;

    if (THIS->cpid)
	creator = find_task_by_pid_type(PIDTYPE_PID, THIS->cpid);
    if (creator)
	THIS->__retvalue = creator->time_slice;
    else
	THIS->__retvalue = 0;
%}

probe kernel.function("sched_exit")
{
	if (is_my_testpro(kernel_string($p->comm)))
		printf("sched_exit/enter:  pid = %d, tgid = %d, ppid = %d, creator = %d, avail. timeslice = %d, creator's timeslice = %d\n",
		    $p->pid, $p->tgid, $p->parent->pid, $p->cpid, $p->time_slice, get_creators_timeslice($p->cpid));
}

probe kernel.function("sched_exit").return
{
	if (is_my_testpro(kernel_string($p->comm)))
		printf("sched_exit/return: pid = %d, tgid = %d, ppid = %d, creator = %d, creator's adjusted timeslice = %d\n",
		    $p->pid, $p->tgid, $p->parent->pid, $p->cpid, get_creators_timeslice($p->cpid)
		);
}

[-- Attachment #4.2: Type: application/pgp-signature, Size: 188 bytes --]

[-- Attachment #5: Type: text/plain, Size: 157 bytes --]



-- 
Vitaly Mayatskikh <vmayatsk@redhat.com>

Kernel development
Red Hat Czech, Brno

Phone: +420 532 294 111
IRC: vitaly on #kernel, #brno
GPG: 0x4BA2E8FB

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

[Michal Schmidt]

Vitaly Mayatskikh skrev:
> 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.

I don't see the point of sending patches for old Linux versions such as 
2.6.21, unless it's something applicable to the -stable tree.
Do recent kernels with CFS have the same problem?

> Patch fixes this issue and
> doesn't break kabi as does the patch from reporter:
> http://lkml.org/lkml/2007/4/7/21

There's no kabi.

Michal

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

[Peter Zijlstra]

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.

>  #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 :-)

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

[Peter Zijlstra]

On Thu, 2007-08-30 at 10:37 +0200, Michal Schmidt wrote:
> Vitaly Mayatskikh skrev:
> > 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.
> 
> I don't see the point of sending patches for old Linux versions such as 
> 2.6.21, unless it's something applicable to the -stable tree.

The older trees might want to have this, perhaps the .16 by Adrian,
certainly distros still care.

> Do recent kernels with CFS have the same problem?

Very much not comparable, as you probably guessed :-)

> > Patch fixes this issue and
> > doesn't break kabi as does the patch from reporter:
> > http://lkml.org/lkml/2007/4/7/21
> 
> There's no kabi.

True.

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

[Pavel Emelyanov]

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 :-)
> 
> 

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

[Oleg Nesterov]

On 08/30, 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.

I agree, "struct pid*" is better, because

	1. we don't need a costly find_pid() in sched_exit()
	2. we don't suffer from pid re-use problem

> >  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);

sched_exit() was removed in 2.6.23-rc.

If you are going to re-introduce this logic, please don't do sched_exit()
from release_task(). It was done this way just because we can't access
->parent after release_task(). But release_task() is called either too
early, or too late for timeslice accounting, depending on ->exit_signal == -1.

I'd suggest to do this in do_exit(), before the last schedule(). Without
write_unlock_irq() the code above needs a couple of rcu_read_lock()'s.

I am not sure Ingo will like this change though...

Oleg.

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

[Peter Zijlstra]

On Thu, 2007-08-30 at 13:49 +0400, Oleg Nesterov wrote:
> On 08/30, 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.
> 
> I agree, "struct pid*" is better, because
> 
> 	1. we don't need a costly find_pid() in sched_exit()
> 	2. we don't suffer from pid re-use problem

Ah, good arguments indeed.

> > >  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);
> 
> sched_exit() was removed in 2.6.23-rc.
> 
> If you are going to re-introduce this logic, please don't do sched_exit()
> from release_task(). It was done this way just because we can't access
> ->parent after release_task(). But release_task() is called either too
> early, or too late for timeslice accounting, depending on ->exit_signal == -1.
> 
> I'd suggest to do this in do_exit(), before the last schedule(). Without
> write_unlock_irq() the code above needs a couple of rcu_read_lock()'s.
> 
> I am not sure Ingo will like this change though...

This is not intended as re-introduction of the feature, this stems from
fixing this issue in older (read distro) kernels.

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

[Oleg Nesterov]

On 08/30, Peter Zijlstra wrote:
>
> On Thu, 2007-08-30 at 13:49 +0400, Oleg Nesterov wrote:
> > 
> > sched_exit() was removed in 2.6.23-rc.
> > 
> > If you are going to re-introduce this logic, please don't do sched_exit()
> > from release_task(). It was done this way just because we can't access
> > ->parent after release_task(). But release_task() is called either too
> > early, or too late for timeslice accounting, depending on ->exit_signal == -1.
> > 
> > I'd suggest to do this in do_exit(), before the last schedule(). Without
> > write_unlock_irq() the code above needs a couple of rcu_read_lock()'s.
> > 
> > I am not sure Ingo will like this change though...
> 
> This is not intended as re-introduction of the feature, this stems from
> fixing this issue in older (read distro) kernels.

Ah, good, sorry for noise then.

In that case I don't think it makes sense to move sched_exit() to do_exit(),
of course. This doesn't look suitable for the -stable tree.

Oleg.