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McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 14/17] rcutorture: Adjust number of reader kthreads per CPU-hotplug operations Date: Wed, 29 Aug 2018 14:47:47 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180829214722.GA23411@linux.vnet.ibm.com> References: <20180829214722.GA23411@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18082921-2213-0000-0000-000002E504A6 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009636; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01080727; UDB=6.00557487; IPR=6.00860712; MB=3.00023001; MTD=3.00000008; XFM=3.00000015; UTC=2018-08-29 21:47:56 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18082921-2214-0000-0000-00005B601550 Message-Id: <20180829214750.26972-14-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-08-29_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1808290211 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, rcutorture provisions rcu_torture_reader() kthreads based on the initial number of CPUs. This can be problematic when CPU hotplug is enabled, as a system with a very large number of CPUs will provision a very large number of rcu_torture_reader() kthreads. All of these kthreads will continue running even if the CPU-hotplug operations result in only one remaining online CPU. This can result in all sorts of strange artifacts due simply to massive overload. This commit therefore causes the rcu_torture_reader() kthreads to start blocking as the number of online CPUs decreases. This is accomplished by numbering these kthreads, and having each check to make sure that the number of online CPUs is at least as large as its assigned number. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index ac487ea8d245..50015b78a43f 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -1400,6 +1400,8 @@ static int rcu_torture_reader(void *arg) { unsigned long lastsleep = jiffies; + long myid = (long)arg; + int mynumonline = myid; DEFINE_TORTURE_RANDOM(rand); struct timer_list t; @@ -1419,6 +1421,8 @@ rcu_torture_reader(void *arg) schedule_timeout_interruptible(1); lastsleep = jiffies + 10; } + while (num_online_cpus() < mynumonline && !torture_must_stop()) + schedule_timeout_interruptible(HZ / 5); stutter_wait("rcu_torture_reader"); } while (!torture_must_stop()); if (irqreader && cur_ops->irq_capable) { @@ -2063,7 +2067,7 @@ static void rcu_test_debug_objects(void) static int __init rcu_torture_init(void) { - int i; + long i; int cpu; int firsterr = 0; static struct rcu_torture_ops *torture_ops[] = { @@ -2169,7 +2173,7 @@ rcu_torture_init(void) goto unwind; } for (i = 0; i < nrealreaders; i++) { - firsterr = torture_create_kthread(rcu_torture_reader, NULL, + firsterr = torture_create_kthread(rcu_torture_reader, (void *)i, reader_tasks[i]); if (firsterr) goto unwind; -- 2.17.1