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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-01-03 16:42:18 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-03-31 13:34:49 -0700
commitfcfd0a237bfcf0c314005007e9d76e55a25e2bad (patch)
treefd7984d324b09a4d4ef8662eec232b64bb80d703 /kernel/rcu
parent86057b80ae31d37fcbdb5f57d15aaf1148c69f96 (diff)
downloadlinux-sh-fcfd0a237bfcf0c314005007e9d76e55a25e2bad.tar.gz
rcu: Make FQS schedule advance only if FQS happened
Currently, the force-quiescent-state (FQS) code in rcu_gp_kthread() can advance the next FQS even if one was not executed last time. This can happen due timeout-duration uncertainty. This commit therefore avoids advancing the FQS schedule unless an FQS was just executed. In the corner case where an FQS was not executed, but is due now, the code does a one-jiffy wait. This change prepares for kthread kicking. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c23
1 files changed, 15 insertions, 8 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a327a253c178..6116cfad18ff 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2146,6 +2146,15 @@ static int __noreturn rcu_gp_kthread(void *arg)
TPS("fqsend"));
cond_resched_rcu_qs();
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_rcu_qs();
@@ -2154,14 +2163,12 @@ static int __noreturn rcu_gp_kthread(void *arg)
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqswaitsig"));
- }
- 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;
+ ret = 1; /* Keep old FQS timing. */
+ j = jiffies;
+ if (time_after(jiffies, rsp->jiffies_force_qs))
+ j = 1;
+ else
+ j = rsp->jiffies_force_qs - j;
}
}