Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1414725 > unrolled thread

[PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups Yuyang Du <yuyang.du@intel.com> - 2016-06-06 10:20 +0200
    Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task  when changing task groups Peter Zijlstra <peterz@infradead.org> - 2016-06-06 12:00 +0200
    Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task  when changing task groups Matt Fleming <matt@codeblueprint.co.uk> - 2016-06-06 16:10 +0200
      Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task  when changing task groups Yuyang Du <yuyang.du@intel.com> - 2016-06-07 05:20 +0200

#1414725 — [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups

Newly forked task has not been enqueued, so should not be removed from
cfs_rq in task_move_group_fair(). To do so, we need to pass the fork
information all the way from sched_move_task() to task_move_group_fair().

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
---
 kernel/sched/auto_group.c |    2 +-
 kernel/sched/core.c       |    8 ++++----
 kernel/sched/fair.c       |    8 ++++++--
 kernel/sched/sched.h      |    4 ++--
 4 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index a5d966c..15f2eb7 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -143,7 +143,7 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
 		goto out;
 
 	for_each_thread(p, t)
-		sched_move_task(t);
+		sched_move_task(t, false);
 out:
 	unlock_task_sighand(p, &flags);
 	autogroup_kref_put(prev);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7f2cae4..ae5b8a8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7724,7 +7724,7 @@ void sched_offline_group(struct task_group *tg)
  *	by now. This function just updates tsk->se.cfs_rq and tsk->se.parent to
  *	reflect its new group.
  */
-void sched_move_task(struct task_struct *tsk)
+void sched_move_task(struct task_struct *tsk, bool fork)
 {
 	struct task_group *tg;
 	int queued, running;
@@ -7753,7 +7753,7 @@ void sched_move_task(struct task_struct *tsk)
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	if (tsk->sched_class->task_move_group)
-		tsk->sched_class->task_move_group(tsk);
+		tsk->sched_class->task_move_group(tsk, fork);
 	else
 #endif
 		set_task_rq(tsk, task_cpu(tsk));
@@ -8186,7 +8186,7 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
 
 static void cpu_cgroup_fork(struct task_struct *task)
 {
-	sched_move_task(task);
+	sched_move_task(task, true);
 }
 
 static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
@@ -8213,7 +8213,7 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 	struct cgroup_subsys_state *css;
 
 	cgroup_taskset_for_each(task, css, tset)
-		sched_move_task(task);
+		sched_move_task(task, false);
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 28b3415..370e284 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8429,9 +8429,13 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-static void task_move_group_fair(struct task_struct *p)
+static void task_move_group_fair(struct task_struct *p, bool fork)
 {
-	detach_task_cfs_rq(p);
+	/*
+	 * Newly forked task should not be removed from any cfs_rq
+	 */
+	if (!fork)
+		detach_task_cfs_rq(p);
 	set_task_rq(p, task_cpu(p));
 	attach_task_cfs_rq(p);
 	/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 72f1f30..c139ec4 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -343,7 +343,7 @@ extern void sched_online_group(struct task_group *tg,
 extern void sched_destroy_group(struct task_group *tg);
 extern void sched_offline_group(struct task_group *tg);
 
-extern void sched_move_task(struct task_struct *tsk);
+extern void sched_move_task(struct task_struct *tsk, bool fork);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
@@ -1247,7 +1247,7 @@ struct sched_class {
 	void (*update_curr) (struct rq *rq);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-	void (*task_move_group) (struct task_struct *p);
+	void (*task_move_group) (struct task_struct *p, bool fork);
 #endif
 };
 
-- 
1.7.9.5

[toc] | [next] | [standalone]

#1414852 — Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups

On Mon, Jun 06, 2016 at 08:20:39AM +0800, Yuyang Du wrote:
> +static void task_move_group_fair(struct task_struct *p, bool fork)
>  {
> -	detach_task_cfs_rq(p);
> +	/*
> +	 * Newly forked task should not be removed from any cfs_rq

That's a pointless comment; that's exactly what the code _does_.
Comments should explain the code, not restate it.

So a comment like:

	 * Newly forked tasks are not attached yet.

Is entirely more useful.

> +	 */
> +	if (!fork)
> +		detach_task_cfs_rq(p);
>  	set_task_rq(p, task_cpu(p));
>  	attach_task_cfs_rq(p);
>  	/*

[toc] | [prev] | [next] | [standalone]

#1415074 — Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups

On Mon, 06 Jun, at 08:20:39AM, Yuyang Du wrote:
> Newly forked task has not been enqueued, so should not be removed from
> cfs_rq in task_move_group_fair(). To do so, we need to pass the fork
> information all the way from sched_move_task() to task_move_group_fair().
> 
> Signed-off-by: Yuyang Du <yuyang.du@intel.com>
> ---
>  kernel/sched/auto_group.c |    2 +-
>  kernel/sched/core.c       |    8 ++++----
>  kernel/sched/fair.c       |    8 ++++++--
>  kernel/sched/sched.h      |    4 ++--
>  4 files changed, 13 insertions(+), 9 deletions(-)

[...]

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 28b3415..370e284 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8429,9 +8429,13 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
>  }
>  
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> -static void task_move_group_fair(struct task_struct *p)
> +static void task_move_group_fair(struct task_struct *p, bool fork)
>  {
> -	detach_task_cfs_rq(p);
> +	/*
> +	 * Newly forked task should not be removed from any cfs_rq
> +	 */
> +	if (!fork)
> +		detach_task_cfs_rq(p);
>  	set_task_rq(p, task_cpu(p));
>  	attach_task_cfs_rq(p);
>  	/*

Wouldn't it be more symmetric to add,

	if (p->se.avg.last_update_time)
		__update_load_avg(...)

to detach_entity_load_avg() so that there's no need to pass the @fork
parameter all the way down the stack, and more importantly, remember
to *not* call detach_task_cfs_rq() if the code changes in the future?

Additionally adding the above check looks like it would fix a race
that (I think) occurs if a newly forked task's class is changed before
it is enqueued in wake_up_new_task().

[toc] | [prev] | [next] | [standalone]

#1415653 — Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups

On Mon, Jun 06, 2016 at 03:03:38PM +0100, Matt Fleming wrote:
> >  #ifdef CONFIG_FAIR_GROUP_SCHED
> > -static void task_move_group_fair(struct task_struct *p)
> > +static void task_move_group_fair(struct task_struct *p, bool fork)
> >  {
> > -	detach_task_cfs_rq(p);
> > +	/*
> > +	 * Newly forked task should not be removed from any cfs_rq
> > +	 */
> > +	if (!fork)
> > +		detach_task_cfs_rq(p);
> >  	set_task_rq(p, task_cpu(p));
> >  	attach_task_cfs_rq(p);
> >  	/*
> 
> Wouldn't it be more symmetric to add,
> 
> 	if (p->se.avg.last_update_time)
> 		__update_load_avg(...)
> 
> to detach_entity_load_avg() so that there's no need to pass the @fork
> parameter all the way down the stack

Up to this point, we can't. But we should be able to if we move the next
patch (4/5) before this patch. I should have changed my mindset with that
patch. Good advice though, thanks, Matt.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web