linux-kernel - [PATCH tip/core/rcu 12/24] rcutorture: Avoid RCU CPU stall warning and RT throttling

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Message-Id: <1460475837-26498-12-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 12 Apr 2016 08:43:45 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 12/24] rcutorture: Avoid RCU CPU stall warning and RT throttling

Running rcuperf can result in RCU CPU stall warnings and RT throttling.
These occur because on of the real-time writer processes does
ftrace_dump() while still running at real-time priority.  This commit
therefore prevents these problems by setting the writer thread back to
SCHED_NORMAL (AKA SCHED_OTHER) before doing ftrace_dump().

In addition, this commit adds a small fixed delay before dumping ftrace
buffer in order to decrease the probability that this dumping will
interfere with other writers' grace periods.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/rcuperf.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
index 278600143bb6..4c0572859ff0 100644
--- a/kernel/rcu/rcuperf.c
+++ b/kernel/rcu/rcuperf.c
@@ -404,11 +404,15 @@ rcu_perf_writer(void *arg)
 			started = true;
 		if (!done && i >= MIN_MEAS) {
 			done = true;
+			sp.sched_priority = 0;
+			sched_setscheduler_nocheck(current,
+						   SCHED_NORMAL, &sp);
 			pr_alert("%s" PERF_FLAG
 				 "rcu_perf_writer %ld has %d measurements\n",
 				 perf_type, me, MIN_MEAS);
 			if (atomic_inc_return(&n_rcu_perf_writer_finished) >=
 			    nrealwriters) {
+				schedule_timeout_interruptible(10);
 				rcu_ftrace_dump(DUMP_ALL);
 				PERFOUT_STRING("Test complete");
 				t_rcu_perf_writer_finished = t;
-- 
2.5.2