[PATCH tip/core/rcu 20/27] rcu: Check the range of jiffies_till_{first,next}_fqs when setting them

Paul E. McKenney
2018-06-26T00:34:29Z

From: Byungchul Park <byungchul.park@lge.com>

Currently, the range of jiffies_till_{first,next}_fqs are checked and
adjusted on and on in the loop of rcu_gp_kthread on runtime.

However, it's enough to check them only when setting them, not every
time in the loop. So make them handled on a setting time via sysfs.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcu/tree.c | 45 ++++++++++++++++++++++++++++++++-------------
1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index bc1ed77a3df9..c59cca40ea92 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -510,8 +510,38 @@ static ulong jiffies_till_first_fqs = ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
static bool rcu_kick_kthreads;

-module_param(jiffies_till_first_fqs, ulong, 0644);
-module_param(jiffies_till_next_fqs, ulong, 0644);
+static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
+{
+ ulong j;
+ int ret = kstrtoul(val, 0, &j);
+
+ if (!ret)
+ WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
+ return ret;
+}
+
+static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
+{
+ ulong j;
+ int ret = kstrtoul(val, 0, &j);
+
+ if (!ret)
+ WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
+ return ret;
+}
+
+static struct kernel_param_ops first_fqs_jiffies_ops = {
+ .set = param_set_first_fqs_jiffies,
+ .get = param_get_ulong,
+};
+
+static struct kernel_param_ops next_fqs_jiffies_ops = {
+ .set = param_set_next_fqs_jiffies,
+ .get = param_get_ulong,
+};
+
+module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
+module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
module_param(rcu_kick_kthreads, bool, 0644);

/*
@@ -2180,10 +2210,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
/* Handle quiescent-state forcing. */
first_gp_fqs = true;
j = jiffies_till_first_fqs;
- if (j > HZ) {
- j = HZ;
- jiffies_till_first_fqs = HZ;
- }
ret = 0;
for (;;) {
if (!ret) {
@@ -2218,13 +2244,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
WRITE_ONCE(rsp->gp_activity, jiffies);
ret = 0; /* Force full wait till next FQS. */
j = jiffies_till_next_fqs;
- if (j > HZ) {
- j = HZ;
- jiffies_till_next_fqs = HZ;
- } else if (j < 1) {
- j = 1;
- jiffies_till_next_fqs = 1;
- }
} else {
/* Deal with stray signal. */
cond_resched_tasks_rcu_qs();
--
2.17.1