On Sun, Jun 10, 2018 at 04:45:43PM -0700, Joel Fernandes wrote:
> From: "Joel Fernandes (Google)" <[email protected]>
>
> 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) <[email protected]>
Thank you, Joel! I have queued these for testing and review.
Peter Zijlstra might have some feedback on variable access, but will
test first.
Thanx, Paul
> ---
> kernel/rcu/rcutorture.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 5219e7ccd8a4..00e06349d7bb 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -55,6 +55,7 @@
> #include <linux/torture.h>
> #include <linux/vmalloc.h>
> #include <linux/sched/debug.h>
> +#include <linux/sched/sysctl.h>
>
> #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;
> @@ -1510,6 +1537,7 @@ 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! */
> @@ -1526,6 +1554,7 @@ 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),
> --
> 2.18.0.rc1.242.g61856ae69a-goog
>
