From 450efca7182a516a12dfcc0311abfd242bde42b2 Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Sun, 10 Jun 2018 16:45:43 -0700 Subject: [PATCH] rcutorture: Disable RT throttling for boost tests Currently rcutorture is not able to torture RCU boosting properly. This is because the rcutorture's boost threads which are doing the torturing may be throttled due to RT throttling. This patch makes rcutorture use the right torture technique (unthrottled rcutorture boost tasks) for torturing RCU so that the test fails correctly when no boost is available. Currently this requires accessing sysctl_sched_rt_runtime directly, but that should be Ok since rcutorture is test code. Such direct access is also only possible if rcutorture is used as a built-in so make it conditional on that. Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index aa0be7ec2a26..74e47d0a618c 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -55,6 +55,7 @@ #include #include #include +#include #include "rcu.h" @@ -772,6 +773,32 @@ static void rcu_torture_boost_cb(struct rcu_head *head) smp_store_release(&rbip->inflight, 0); } +static int old_rt_runtime = -1; + +static void rcu_torture_disable_rt_throttle(void) +{ + /* + * Disable RT throttling so that rcutorture's boost threads don't get + * throttled. Only possible if rcutorture is built-in otherwise the + * user should manually do this by setting the sched_rt_period_us and + * sched_rt_runtime sysctls. + */ + if (!IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) || old_rt_runtime != -1) + return; + + old_rt_runtime = sysctl_sched_rt_runtime; + sysctl_sched_rt_runtime = -1; +} + +static void rcu_torture_enable_rt_throttle(void) +{ + if (!IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) || old_rt_runtime == -1) + return; + + sysctl_sched_rt_runtime = old_rt_runtime; + old_rt_runtime = -1; +} + static int rcu_torture_boost(void *arg) { unsigned long call_rcu_time; @@ -1511,6 +1538,7 @@ static int rcutorture_booster_cleanup(unsigned int cpu) mutex_lock(&boost_mutex); t = boost_tasks[cpu]; boost_tasks[cpu] = NULL; + rcu_torture_enable_rt_throttle(); mutex_unlock(&boost_mutex); /* This must be outside of the mutex, otherwise deadlock! */ @@ -1527,6 +1555,7 @@ static int rcutorture_booster_init(unsigned int cpu) /* Don't allow time recalculation while creating a new task. */ mutex_lock(&boost_mutex); + rcu_torture_disable_rt_throttle(); VERBOSE_TOROUT_STRING("Creating rcu_torture_boost task"); boost_tasks[cpu] = kthread_create_on_node(rcu_torture_boost, NULL, cpu_to_node(cpu), -- 2.30.2