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Subject[PATCH] rcu/nocb: Avoid polling when myrdp->nocb_head_rdp list is empty
Date
Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog kthreads
enter polling mode. however, due to only insert CPU's rdp which belong to
rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp served by rcuog
kthread have been de-offloaded, these cause the 'nocb_head_rdp' list
served by rcuog kthread is empty, when the 'nocb_head_rdp' is empty,
the rcuog kthread in polling mode not actually do anything. fix it by
exiting polling mode when the 'nocb_head_rdp'list is empty, otherwise
entering polling mode.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
kernel/rcu/tree_nocb.h | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index fa8e4f82e60c..c25c3e3dd22d 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
TPS("WakeBypassIsDeferred"));
}
if (rcu_nocb_poll) {
- /* Polling, so trace if first poll in the series. */
- if (gotcbs)
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
- schedule_timeout_idle(1);
+ if (list_empty(&my_rdp->nocb_head_rdp)) {
+ rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
+ } else {
+ /* Polling, so trace if first poll in the series. */
+ if (gotcbs)
+ trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
+ schedule_timeout_idle(1);
+ }
} else if (!needwait_gp) {
/* Wait for callbacks to appear. */
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
@@ -980,7 +984,7 @@ static int rdp_offload_toggle(struct rcu_data *rdp,
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
// Queue this rdp for add/del to/from the list to iterate on rcuog
WRITE_ONCE(rdp_gp->nocb_toggling_rdp, rdp);
- if (rdp_gp->nocb_gp_sleep) {
+ if (rcu_nocb_poll || rdp_gp->nocb_gp_sleep) {
rdp_gp->nocb_gp_sleep = false;
wake_gp = true;
}
--
2.25.1
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