Re: [tip:sched/core] sched: Add 'autogroup' scheduling feature: automated per session task groups

[Bharata B Rao <bharata.rao@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1658 bytes --]

On Mon, Dec 20, 2010 at 6:49 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Mon, 2010-12-20 at 18:38 +0530, Bharata B Rao wrote:
>> The autogroup patchset removes the display of cgroup name from
>> sched_debug output.
>
> Hrmph.. that wasn't supposed to happen, care to send a patch to fix that
> up?

There are two aspects here:

- Printing cgroup name for per-CPU cfs_rqs shouldn't be affected by
  autogroup and the old code should work here.
- Printing cgroup name for tasks depends on task_group(), which has
been changed by autogroup patch. I haven't really looked deep into
autogroup patch, but from whatever I can gather, Mike had a reason
to remove this bit from sched_debug. The task groups created for
autogroups don't have cgroups associated with them and hence no
dentries and hence no pathnames.

I guess we could do fix this as shown in the attached patch.

>
>
>> Also, with tg_shares_up improvements, the leaf cfs_rqs are maintained
>> on rq->leaf_cfs_rq_list only if they carry any load. But the code to
>> display cfs_rq information for sched_debug isn't updated and hence
>> information from a few cfs_rqs are missing from sched_debug.
>
> Well, that's a _good_ thing, right?
>
> I mean, if we know they're empty, and don't contribute to schedule, why
> bother displaying them?

In addition to tasks, we do display other details pertaining to the cfs_rq.
I thought, having a complete view of all the cfs_rqs in the system would
be better and consistent than obtaining different cfs_rqs on different
captures of /proc/sched_debug.

Regards,
Bharata.
-- 
http://bharata.sulekha.com/blog/posts.htm, http://raobharata.wordpress.com/

[-- Attachment #2: fix-sched-debug.patch --]
[-- Type: application/octet-stream, Size: 2636 bytes --]

Re-instate cgroup names in /proc/sched_debug.

Autogroup patch removed displaying the cgroup pathnames
for per-CPU cfs_rqs and tasks in /proc/sched_debug.
Re-instate this.

Signed-off-by: Bharata B Rao <bharata.rao@gmail.com>

Index: linux-2.6-tip/kernel/sched_debug.c
===================================================================
--- linux-2.6-tip.orig/kernel/sched_debug.c	2010-12-11 01:25:58.000000000 +0530
+++ linux-2.6-tip/kernel/sched_debug.c	2010-12-21 02:23:05.000000000 +0530
@@ -86,6 +86,25 @@
 }
 #endif
 
+#if defined(CONFIG_CGROUP_SCHED) && \
+	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
+/*
+ * This is essentially same as sched.c:task_group except
+ * that it doesn't bother about autogroups. Essentially
+ * this is how task_group() looked like before autogroup
+ * changes.
+ * Named task_sched_group() for want of a better name.
+ */
+static struct task_group *task_sched_group(struct task_struct *p)
+{
+	struct cgroup_subsys_state *css;
+
+	css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
+			lockdep_is_held(&task_rq(p)->lock));
+	return container_of(css, struct task_group, css);
+}
+#endif
+
 static void
 print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 {
@@ -108,6 +127,16 @@
 	SEQ_printf(m, "%15Ld %15Ld %15Ld.%06ld %15Ld.%06ld %15Ld.%06ld",
 		0LL, 0LL, 0LL, 0L, 0LL, 0L, 0LL, 0L);
 #endif
+#ifdef CONFIG_CGROUP_SCHED
+	{
+		char path[64];
+
+		rcu_read_lock();
+		cgroup_path(task_sched_group(p)->css.cgroup, path, sizeof(path));
+		rcu_read_unlock();
+		SEQ_printf(m, " %s", path);
+	}
+#endif
 
 	SEQ_printf(m, "\n");
 }
@@ -136,6 +165,19 @@
 	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,
@@ -144,7 +186,16 @@
 	struct sched_entity *last;
 	unsigned long flags;
 
+#if defined(CONFIG_CGROUP_SCHED) && defined(CONFIG_FAIR_GROUP_SCHED)
+	char path[128];
+	struct task_group *tg = cfs_rq->tg;
+
+	task_group_path(tg, path, sizeof(path));
+
+	SEQ_printf(m, "\ncfs_rq[%d]:%s\n", cpu, path);
+#else
 	SEQ_printf(m, "\ncfs_rq[%d]:\n", cpu);
+#endif
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "exec_clock",
 			SPLIT_NS(cfs_rq->exec_clock));