[PATCH rcu 3/7] rcuscale: Console output claims too few grace periods

Paul E. McKenney
2021-07-21T21:04:52Z

From: "Jiangong.Han" <jiangong.han@windriver.com>

The rcuscale console output claims N grace periods, numbered from zero
to N, which means that there were really N+1 grace periods. The root
cause of this bug is that rcu_scale_writer() stores the number of the
last grace period (numbered from zero) into writer_n_durations[me]
instead of the number of grace periods. This commit therefore assigns
the actual number of grace periods to writer_n_durations[me], and also
makes the corresponding adjustment to the loop outputting per-grace-period
measurements.

Sample of old console output:
rcu-scale: writer 0 gps: 133
......
rcu-scale: 0 writer-duration: 0 44003961
rcu-scale: 0 writer-duration: 1 32003582
......
rcu-scale: 0 writer-duration: 132 28004391
rcu-scale: 0 writer-duration: 133 27996410

Sample of new console output:
rcu-scale: writer 0 gps: 134
......
rcu-scale: 0 writer-duration: 0 44003961
rcu-scale: 0 writer-duration: 1 32003582
......
rcu-scale: 0 writer-duration: 132 28004391
rcu-scale: 0 writer-duration: 133 27996410

Signed-off-by: Jiangong.Han <jiangong.han@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/rcuscale.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index dca51fe9c73f2..2cc34a22a5060 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -487,7 +487,7 @@ rcu_scale_writer(void *arg)
if (gp_async) {
cur_ops->gp_barrier();
}
- writer_n_durations[me] = i_max;
+ writer_n_durations[me] = i_max + 1;
torture_kthread_stopping("rcu_scale_writer");
return 0;
}
@@ -561,7 +561,7 @@ rcu_scale_cleanup(void)
wdpp = writer_durations[i];
if (!wdpp)
continue;
- for (j = 0; j <= writer_n_durations[i]; j++) {
+ for (j = 0; j < writer_n_durations[i]; j++) {
wdp = &wdpp[j];
pr_alert("%s%s %4d writer-duration: %5d %llu\n",
scale_type, SCALE_FLAG,
--
2.31.1.189.g2e36527f23