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

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Mon, 2010-11-15 at 17:55 -0800, Paul Menage wrote:
> On Mon, Nov 15, 2010 at 5:18 PM, Linus Torvalds
> <torvalds@linux-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() ?

Right, that doesn't solve the full problem though.

/proc/sched_debug should show these automagic task_groups, its just that
there's currently no way to properly name them, we can of course add
something like a name field to the struct autogroup thing, but what do
we fill it with? "autogroup-%d" and keep a sequence number for each
autogroup?

Then the below task_group_path() thing can try the autogroup name scheme
if it finds a NULL css.

Something like the below might avoid the explosion:

---
 kernel/sched_debug.c |   28 ++++++++++++++--------------
 1 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 2e1b0d1..9b5560f 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -87,6 +87,19 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu,
 }
 #endif
 
+#if defined(CONFIG_CGROUP_SCHED) && \
+	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
+static void task_group_path(struct task_group *tg, char *buf, int buflen)
+{
+	/* may be NULL if the underlying cgroup isn't fully-created yet */
+	if (!tg->css.cgroup) {
+		buf[0] = '\0';
+		return;
+	}
+	cgroup_path(tg->css.cgroup, buf, buflen);
+}
+#endif
+
 static void
 print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 {
@@ -115,7 +128,7 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 		char path[64];
 
 		rcu_read_lock();
-		cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
+		task_group_path(task_group(p), path, sizeof(path));
 		rcu_read_unlock();
 		SEQ_printf(m, " %s", path);
 	}
@@ -147,19 +160,6 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 	read_unlock_irqrestore(&tasklist_lock, flags);
 }
 
-#if defined(CONFIG_CGROUP_SCHED) && \
-	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
-static void task_group_path(struct task_group *tg, char *buf, int buflen)
-{
-	/* may be NULL if the underlying cgroup isn't fully-created yet */
-	if (!tg->css.cgroup) {
-		buf[0] = '\0';
-		return;
-	}
-	cgroup_path(tg->css.cgroup, buf, buflen);
-}
-#endif
-
 void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 {
 	s64 MIN_vruntime = -1, min_vruntime, max_vruntime = -1,