linux-kernel - Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

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Message-ID: <1289912299.5169.53.camel@maggy.simson.net>
Date:	Tue, 16 Nov 2010 05:58:19 -0700
From:	Mike Galbraith <efault@....de>
To:	Paul Menage <menage@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Valdis.Kletnieks@...edu, Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Daniel Lezcano <daniel.lezcano@...e.fr>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

On Mon, 2010-11-15 at 17:55 -0800, Paul Menage wrote:
> On Mon, Nov 15, 2010 at 5:18 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > so sched_debug_show() is apparently calling cgroup_path() with a NULL
> > cgroup. I think it's "print_task()" that is to blame, it does
> >
> >     cgroup_path(task_group(p)->css.cgroup, ..
> >
> > without checking whether there _is_ any css.cgroup.
> 
> Right - previously the returned task_group would be always associated
> with a cgroup. Now, it may not be.
> 
> The original task_group() should be made accessible for anything that
> wants a real cgroup in the scheduler hierarchy, and called from the
> new task_group() function. Not sure what the best naming convention
> would be, maybe task_group() and effective_task_group() ?

effective_task_group() works for me.  Autogroup (currently at least)
only needs to interface with set_task_rq().

A tasty alternative would be to have autogroup be it's own subsystem,
with full cgroup userspace visibility/tweakability.  I have no idea if
that's feasible though.  I glanced at cgroup.c, but didn't see the dirt
simple I wanted, and quickly ran away. 

---
 kernel/sched.c |   20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -606,27 +606,33 @@ static inline int cpu_of(struct rq *rq)
  */
 static inline struct task_group *task_group(struct task_struct *p)
 {
-	struct task_group *tg;
 	struct cgroup_subsys_state *css;
 
 	css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
 			lockdep_is_held(&task_rq(p)->lock));
-	tg = container_of(css, struct task_group, css);
+	return container_of(css, struct task_group, css);
+}
 
-	return autogroup_task_group(p, tg);
+static inline struct task_group *effective_task_group(struct task_struct *p)
+{
+	return autogroup_task_group(p, task_group(p));
 }
 
 /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
 static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 {
+#if (defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
+	struct task_group *tg = effective_task_group(p);
+#endif
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
-	p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
-	p->se.parent = task_group(p)->se[cpu];
+	p->se.cfs_rq = tg->cfs_rq[cpu];
+	p->se.parent = tg->se[cpu];
 #endif
 
 #ifdef CONFIG_RT_GROUP_SCHED
-	p->rt.rt_rq  = task_group(p)->rt_rq[cpu];
-	p->rt.parent = task_group(p)->rt_se[cpu];
+	p->rt.rt_rq  = tg->rt_rq[cpu];
+	p->rt.parent = tg->rt_se[cpu];
 #endif
 }
 


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