[PATCH v3 tip/core/rcu 31/34] rcu-tasks: Add rcu_dynticks_zero_in_eqs() effectiveness statistics

paulmck
2020-03-27T22:25:54Z

This commit adds counts of the number of calls and number of successful
calls to rcu_dynticks_zero_in_eqs(), which are printed at the end
of rcutorture runs and at stall time. This allows evaluation of the
effectiveness of rcu_dynticks_zero_in_eqs().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tasks.h | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 27d2458..c1a0706 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -725,6 +725,11 @@ DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks.
// Record outstanding IPIs to each CPU. No point in sending two...
static DEFINE_PER_CPU(bool, trc_ipi_to_cpu);

+// The number of detections of task quiescent state relying on
+// heavyweight readers executing explicit memory barriers.
+unsigned long n_heavy_reader_attempts;
+unsigned long n_heavy_reader_updates;
+
void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
"RCU Tasks Trace");
@@ -830,9 +835,11 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
// If heavyweight readers are enabled on the remote task,
// we can inspect its state despite its currently running.
// However, we cannot safely change its state.
+ n_heavy_reader_attempts++;
if (!ofl && // Check for "running" idle tasks on offline CPUs.
!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
return false; // No quiescent state, do it the hard way.
+ n_heavy_reader_updates++;
in_qs = true;
} else {
in_qs = likely(!t->trc_reader_nesting);
@@ -1143,9 +1150,11 @@ core_initcall(rcu_spawn_tasks_trace_kthread);

static void show_rcu_tasks_trace_gp_kthread(void)
{
- char buf[32];
+ char buf[64];

- sprintf(buf, "N%d", atomic_read(&trc_n_readers_need_end));
+ sprintf(buf, "N%d h:%lu/%lu", atomic_read(&trc_n_readers_need_end),
+ data_race(n_heavy_reader_updates),
+ data_race(n_heavy_reader_attempts));
show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf);
}

--
2.9.5