linux-kernel - [PATCH] sched/deadline: Update total bandwidth when adding new task

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Date:	Tue, 18 Feb 2014 21:56:59 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] sched/deadline: Update total bandwidth when adding new task

While debugging the crash with the bad nr_running accounting, I hit
another bug where, after running my sched deadline test, I was getting
failures to take a CPU offline. It was giving me a -EBUSY error.

Adding a bunch of trace_printk()s around, I found that the cpu
notifier that called sched_cpu_inactive() was returning a failure. The
overflow value was coming up negative?

Adding more trace_printk()s, I found that task_dead_dl() function was
subtracting the exact amount that was keeping the CPU from going
offline. I then realized that the task_dead_dl() was updating the
total_bw for the task that was going away, but there was nothing that
added to the total_bw when the task came alive. If total_bw is not
zero for a CPU, it will keep that CPU from going offline.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b46131e..17f4830 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3178,6 +3178,7 @@ static void
 __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
 {
 	struct sched_dl_entity *dl_se = &p->dl;
+	struct dl_bw *dl_b = dl_bw_of(task_cpu(p));

 	init_dl_task_timer(dl_se);
 	dl_se->dl_runtime = attr->sched_runtime;
@@ -3187,6 +3188,7 @@ __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
 	dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
 	dl_se->dl_throttled = 0;
 	dl_se->dl_new = 1;
+	__dl_add(dl_b, dl_se->dl_bw);
 }

 /* Actually do priority change: must hold pi & rq lock. */
--
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