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Subject[PATCH] rcu: Only boost rcu reader tasks with lower priority than boost kthreads
Date
When RCU_BOOST is enabled, the boost kthreads will boosting readers
who are blocking a given grace period, if the current reader tasks
have a higher priority than boost kthreads(the boost kthreads priority
not always 1, if the kthread_prio is set), boosting is useless, skip
current task and select next task to boosting, reduce the time for a
given grace period.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
kernel/rcu/tree_plugin.h | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c3d212bc5338..d35b6da66bbd 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -12,6 +12,7 @@
*/

#include "../locking/rtmutex_common.h"
+#include <linux/sched/deadline.h>

static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
{
@@ -1065,13 +1066,20 @@ static int rcu_boost(struct rcu_node *rnp)
* section.
*/
t = container_of(tb, struct task_struct, rcu_node_entry);
+ if (!rnp->exp_tasks && (dl_task(t) || t->prio <= current->prio)) {
+ tb = rcu_next_node_entry(t, rnp);
+ WRITE_ONCE(rnp->boost_tasks, tb);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ goto end;
+ }
+
rt_mutex_init_proxy_locked(&rnp->boost_mtx.rtmutex, t);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/* Lock only for side effect: boosts task t's priority. */
rt_mutex_lock(&rnp->boost_mtx);
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
rnp->n_boosts++;
-
+end:
return READ_ONCE(rnp->exp_tasks) != NULL ||
READ_ONCE(rnp->boost_tasks) != NULL;
}
--
2.25.1
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