[PATCH] sched/debug: Add tracepoint for RT throttling

[PATCH] sched/debug: Add tracepoint for RT throttling

[Benjamin Bouvier]

As there is currently no information on which RT task is throttled, add a
new tracepoint for debug purpose. By the way improve printk debugging
message by adding task name, pid and cpu for which the throttle has been
executed.

Signed-off-by: Benjamin Bouvier <benjamin.bouvier@nokia.com>
---
 include/trace/events/sched.h | 27 +++++++++++++++++++++++++++
 kernel/sched/rt.c            |  6 +++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 9a4bdfadab07..09d3f7566f0a 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -587,6 +587,33 @@ TRACE_EVENT(sched_wake_idle_without_ipi,
 
 	TP_printk("cpu=%d", __entry->cpu)
 );
+
+/*
+ * Tracepoint for RT throttling task.
+ */
+TRACE_EVENT(sched_rt_throttling,
+
+	TP_PROTO(struct task_struct *tsk, int cpu),
+
+	TP_ARGS(tsk, cpu),
+
+	TP_STRUCT__entry(
+		__array(char,	comm,	TASK_COMM_LEN)
+		__field(pid_t,	pid)
+		__field(int,	cpu)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
+		__entry->pid	= tsk->pid;
+		__entry->cpu	= cpu;
+	),
+
+	TP_printk("comm=%s pid=%d cpu=%d",
+			__entry->comm, __entry->pid,
+			__entry->cpu)
+);
+
 #endif /* _TRACE_SCHED_H */
 
 /* This part must be outside protection */
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index a21ea6021929..1a0ee91c9e16 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -6,6 +6,7 @@
 #include "sched.h"
 
 #include "pelt.h"
+#include <trace/events/sched.h>
 
 int sched_rr_timeslice = RR_TIMESLICE;
 int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;
@@ -928,7 +929,10 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 		 */
 		if (likely(rt_b->rt_runtime)) {
 			rt_rq->rt_throttled = 1;
-			printk_deferred_once("sched: RT throttling activated\n");
+			printk_deferred_once(
+				"sched: RT throttling activated for task pid %d (%s) on cpu:%d\n",
+				rt_rq->rq->curr->pid, rt_rq->rq->curr->comm, rt_rq->rq->cpu);
+			trace_sched_rt_throttling(rt_rq->rq->curr, rt_rq->rq->cpu);
 		} else {
 			/*
 			 * In case we did anyway, make it go away,
-- 
2.10.2

Re: [PATCH] sched/debug: Add tracepoint for RT throttling

[Sebastian Andrzej Siewior]

On 2018-12-14 10:27:41 [+0200], Benjamin Bouvier wrote:
> As there is currently no information on which RT task is throttled, add a
> new tracepoint for debug purpose. By the way improve printk debugging
> message by adding task name, pid and cpu for which the throttle has been
> executed.

Throttling is for _all_ RT class applications. The task you print might
be innocent and getting the blame. The interesting part is to see all
the RT tasks (not sure about DL) since the last time, the timer was
started on the CPU.

Sebastian

Re: [PATCH] sched/debug: Add tracepoint for RT throttling

[kbuild test robot]

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Hi Benjamin,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tip/perf/core]
[also build test ERROR on v4.20-rc6 next-20181214]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Benjamin-Bouvier/sched-debug-Add-tracepoint-for-RT-throttling/20181216-050740
config: x86_64-randconfig-x001-201850 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   In file included from include/linux/kernel.h:14:0,
                    from arch/x86/include/asm/percpu.h:45,
                    from arch/x86/include/asm/current.h:6,
                    from include/linux/sched.h:12,
                    from kernel//sched/sched.h:5,
                    from kernel//sched/rt.c:6:
   kernel//sched/rt.c: In function 'sched_rt_runtime_exceeded':
>> kernel//sched/rt.c:934:59: error: 'struct rq' has no member named 'cpu'
        rt_rq->rq->curr->pid, rt_rq->rq->curr->comm, rt_rq->rq->cpu);
                                                              ^
   include/linux/printk.h:372:26: note: in definition of macro 'printk_deferred_once'
      printk_deferred(fmt, ##__VA_ARGS__);  \
                             ^~~~~~~~~~~
   kernel//sched/rt.c:935:56: error: 'struct rq' has no member named 'cpu'
       trace_sched_rt_throttling(rt_rq->rq->curr, rt_rq->rq->cpu);
                                                           ^~

vim +934 kernel//sched/rt.c

   907	
   908	static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
   909	{
   910		u64 runtime = sched_rt_runtime(rt_rq);
   911	
   912		if (rt_rq->rt_throttled)
   913			return rt_rq_throttled(rt_rq);
   914	
   915		if (runtime >= sched_rt_period(rt_rq))
   916			return 0;
   917	
   918		balance_runtime(rt_rq);
   919		runtime = sched_rt_runtime(rt_rq);
   920		if (runtime == RUNTIME_INF)
   921			return 0;
   922	
   923		if (rt_rq->rt_time > runtime) {
   924			struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
   925	
   926			/*
   927			 * Don't actually throttle groups that have no runtime assigned
   928			 * but accrue some time due to boosting.
   929			 */
   930			if (likely(rt_b->rt_runtime)) {
   931				rt_rq->rt_throttled = 1;
   932				printk_deferred_once(
   933					"sched: RT throttling activated for task pid %d (%s) on cpu:%d\n",
 > 934					rt_rq->rq->curr->pid, rt_rq->rq->curr->comm, rt_rq->rq->cpu);
   935				trace_sched_rt_throttling(rt_rq->rq->curr, rt_rq->rq->cpu);
   936			} else {
   937				/*
   938				 * In case we did anyway, make it go away,
   939				 * replenishment is a joke, since it will replenish us
   940				 * with exactly 0 ns.
   941				 */
   942				rt_rq->rt_time = 0;
   943			}
   944	
   945			if (rt_rq_throttled(rt_rq)) {
   946				sched_rt_rq_dequeue(rt_rq);
   947				return 1;
   948			}
   949		}
   950	
   951		return 0;
   952	}
   953	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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