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From:   "=?UTF-8?Q?Jan_H._Sch=c3=b6nherr?=" <jschoenh@amazon.de>
Subject: [RFC 00/60] Coscheduling for Linux
To:     Nishanth Aravamudan <naravamudan@digitalocean.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
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On 09/12/2018 09:34 PM, Jan H. Schönherr wrote:
> That said, I see a hang, too. It seems to happen, when there is a
> cpu.scheduled!=0 group that is not a direct child of the root task group.
> You seem to have "/sys/fs/cgroup/cpu/machine" as an intermediate group.
> (The case ==0 within !=0 within the root task group works for me.)
> 
> I'm going to dive into the code.

With the patch below (which technically changes patch 55/60), the hang I experienced is gone.

Please let me know, if it works for you as well.

Regards
Jan


diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8da2033596ff..2d8b3f9a275f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7189,23 +7189,26 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 		while (!(cfs_rq = is_same_group(se, pse))) {
 			int se_depth = se->depth;
 			int pse_depth = pse->depth;
+			bool work = false;

-			if (se_depth <= pse_depth && leader_of(pse) == cpu) {
+			if (se_depth <= pse_depth && __leader_of(pse) == cpu) {
 				put_prev_entity(cfs_rq_of(pse), pse);
 				pse = parent_entity(pse);
+				work = true;
 			}
-			if (se_depth >= pse_depth && leader_of(se) == cpu) {
+			if (se_depth >= pse_depth && __leader_of(se) == cpu) {
 				set_next_entity(cfs_rq_of(se), se);
 				se = parent_entity(se);
+				work = true;
 			}
-			if (leader_of(pse) != cpu && leader_of(se) != cpu)
+			if (!work)
 				break;
 		}

-		if (leader_of(pse) == cpu)
-			put_prev_entity(cfs_rq, pse);
-		if (leader_of(se) == cpu)
-			set_next_entity(cfs_rq, se);
+		if (__leader_of(pse) == cpu)
+			put_prev_entity(cfs_rq_of(pse), pse);
+		if (__leader_of(se) == cpu)
+			set_next_entity(cfs_rq_of(se), se);
 	}

 	goto done;