This commit narrows the scope of each bucket of the forward-progress
callback-invocation histograms from one second to 100 milliseconds, which
aids debugging of forward-progress problems by making shorter-duration
callback-invocation stalls visible.

Signed-off-by: Paul E. McKenney <paul...@linux.ibm.com>
---
 kernel/rcu/rcutorture.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index afa98162575d..a4c4a24bdcaa 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1629,7 +1629,8 @@ static bool rcu_fwd_emergency_stop;
 #define MAX_FWD_CB_JIFFIES     (8 * HZ) /* Maximum CB test duration. */
 #define MIN_FWD_CB_LAUNDERS    3       /* This many CB invocations to count. */
 #define MIN_FWD_CBS_LAUNDERED  100     /* Number of counted CBs. */
-static long n_launders_hist[2 * MAX_FWD_CB_JIFFIES / HZ];
+#define FWD_CBS_HIST_DIV       10      /* Histogram buckets/second. */
+static long n_launders_hist[2 * MAX_FWD_CB_JIFFIES / (HZ / FWD_CBS_HIST_DIV)];
 
 static void rcu_torture_fwd_cb_hist(void)
 {
@@ -1642,7 +1643,8 @@ static void rcu_torture_fwd_cb_hist(void)
        pr_alert("%s: Callback-invocation histogram (duration %lu jiffies):",
                 __func__, jiffies - rcu_fwd_startat);
        for (j = 0; j <= i; j++)
-               pr_cont(" %ds: %ld", j + 1, n_launders_hist[j]);
+               pr_cont(" %ds/%d: %ld",
+                       j + 1, FWD_CBS_HIST_DIV, n_launders_hist[j]);
        pr_cont("\n");
 }
 
@@ -1661,7 +1663,7 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
        rcu_fwd_cb_tail = &rfcp->rfc_next;
        WRITE_ONCE(*rfcpp, rfcp);
        WRITE_ONCE(n_launders_cb, n_launders_cb + 1);
-       i = ((jiffies - rcu_fwd_startat) / HZ);
+       i = ((jiffies - rcu_fwd_startat) / (HZ / FWD_CBS_HIST_DIV));
        if (i >= ARRAY_SIZE(n_launders_hist))
                i = ARRAY_SIZE(n_launders_hist) - 1;
        n_launders_hist[i]++;
-- 
2.17.1

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