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authorIngo Molnar <mingo@kernel.org>2022-03-15 10:28:12 +0100
committerIngo Molnar <mingo@kernel.org>2022-03-15 10:28:12 +0100
commitccdbf33c2349a0a867f46dde5f94b0715f6fa341 (patch)
tree87a4e147e484ed5ebd9e2b4defad7bdcd36b6b37 /kernel/trace/trace_osnoise.c
parentccacfe56d7ecdd2922256b87e9ea46f13bb03b55 (diff)
parent09688c0166e76ce2fb85e86b9d99be8b0084cdf9 (diff)
Merge tag 'v5.17-rc8' into sched/core, to pick up fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/trace/trace_osnoise.c')
-rw-r--r--kernel/trace/trace_osnoise.c84
1 files changed, 63 insertions, 21 deletions
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 1829b4cb8cc1..e9ae1f33a7f0 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1389,6 +1389,26 @@ static int run_osnoise(void)
}
/*
+ * In some cases, notably when running on a nohz_full CPU with
+ * a stopped tick PREEMPT_RCU has no way to account for QSs.
+ * This will eventually cause unwarranted noise as PREEMPT_RCU
+ * will force preemption as the means of ending the current
+ * grace period. We avoid this problem by calling
+ * rcu_momentary_dyntick_idle(), which performs a zero duration
+ * EQS allowing PREEMPT_RCU to end the current grace period.
+ * This call shouldn't be wrapped inside an RCU critical
+ * section.
+ *
+ * Note that in non PREEMPT_RCU kernels QSs are handled through
+ * cond_resched()
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
+ local_irq_disable();
+ rcu_momentary_dyntick_idle();
+ local_irq_enable();
+ }
+
+ /*
* For the non-preemptive kernel config: let threads runs, if
* they so wish.
*/
@@ -1439,6 +1459,37 @@ static struct cpumask osnoise_cpumask;
static struct cpumask save_cpumask;
/*
+ * osnoise_sleep - sleep until the next period
+ */
+static void osnoise_sleep(void)
+{
+ u64 interval;
+ ktime_t wake_time;
+
+ mutex_lock(&interface_lock);
+ interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
+ mutex_unlock(&interface_lock);
+
+ /*
+ * differently from hwlat_detector, the osnoise tracer can run
+ * without a pause because preemption is on.
+ */
+ if (!interval) {
+ /* Let synchronize_rcu_tasks() make progress */
+ cond_resched_tasks_rcu_qs();
+ return;
+ }
+
+ wake_time = ktime_add_us(ktime_get(), interval);
+ __set_current_state(TASK_INTERRUPTIBLE);
+
+ while (schedule_hrtimeout_range(&wake_time, 0, HRTIMER_MODE_ABS)) {
+ if (kthread_should_stop())
+ break;
+ }
+}
+
+/*
* osnoise_main - The osnoise detection kernel thread
*
* Calls run_osnoise() function to measure the osnoise for the configured runtime,
@@ -1446,30 +1497,10 @@ static struct cpumask save_cpumask;
*/
static int osnoise_main(void *data)
{
- u64 interval;
while (!kthread_should_stop()) {
-
run_osnoise();
-
- mutex_lock(&interface_lock);
- interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
- mutex_unlock(&interface_lock);
-
- do_div(interval, USEC_PER_MSEC);
-
- /*
- * differently from hwlat_detector, the osnoise tracer can run
- * without a pause because preemption is on.
- */
- if (interval < 1) {
- /* Let synchronize_rcu_tasks() make progress */
- cond_resched_tasks_rcu_qs();
- continue;
- }
-
- if (msleep_interruptible(interval))
- break;
+ osnoise_sleep();
}
return 0;
@@ -2191,6 +2222,17 @@ static void osnoise_workload_stop(void)
if (osnoise_has_registered_instances())
return;
+ /*
+ * If callbacks were already disabled in a previous stop
+ * call, there is no need to disable then again.
+ *
+ * For instance, this happens when tracing is stopped via:
+ * echo 0 > tracing_on
+ * echo nop > current_tracer.
+ */
+ if (!trace_osnoise_callback_enabled)
+ return;
+
trace_osnoise_callback_enabled = false;
/*
* Make sure that ftrace_nmi_enter/exit() see