linux-kernel - [PATCH 3/6] sched_ext: Make @rf optional for dispatch_to_local

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Message-ID: <20240709212137.1199269-4-tj@kernel.org>
Date: Tue,  9 Jul 2024 11:21:09 -1000
From: Tejun Heo <tj@...nel.org>
To: void@...ifault.com
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	schatzberg.dan@...il.com,
	mingo@...hat.com,
	peterz@...radead.org,
	changwoo@...lia.com,
	righi.andrea@...il.com,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 3/6] sched_ext: Make @rf optional for dispatch_to_local_dsq()

dispatch_to_local_dsq() may unlock the current rq when dispatching to a
local DSQ on a different CPU. This function is currently called from the
balance path where the rq lock is pinned and the associated rq_flags is
available to unpin it.

dispatch_to_local_dsq() will be used to implement direct dispatch to a local
DSQ on a remote CPU from the enqueue path where it will be called with rq
locked but not pinned. Make @rf optional so that the function can be used
from a context which doesn't pin the rq lock.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>
---
 kernel/sched/ext.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 52340ac8038f..e96727460df2 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2040,7 +2040,7 @@ static bool move_task_to_local_dsq(struct rq *rq, struct task_struct *p,
 /**
  * dispatch_to_local_dsq_lock - Ensure source and destination rq's are locked
  * @rq: current rq which is locked
- * @rf: rq_flags to use when unlocking @rq
+ * @rf: optional rq_flags to use when unlocking @rq if its lock is pinned
  * @src_rq: rq to move task from
  * @dst_rq: rq to move task to
  *
@@ -2052,17 +2052,20 @@ static bool move_task_to_local_dsq(struct rq *rq, struct task_struct *p,
 static void dispatch_to_local_dsq_lock(struct rq *rq, struct rq_flags *rf,
 				       struct rq *src_rq, struct rq *dst_rq)
 {
-	rq_unpin_lock(rq, rf);
+	if (rf)
+		rq_unpin_lock(rq, rf);
 
 	if (src_rq == dst_rq) {
 		raw_spin_rq_unlock(rq);
 		raw_spin_rq_lock(dst_rq);
 	} else if (rq == src_rq) {
 		double_lock_balance(rq, dst_rq);
-		rq_repin_lock(rq, rf);
+		if (rf)
+			rq_repin_lock(rq, rf);
 	} else if (rq == dst_rq) {
 		double_lock_balance(rq, src_rq);
-		rq_repin_lock(rq, rf);
+		if (rf)
+			rq_repin_lock(rq, rf);
 	} else {
 		raw_spin_rq_unlock(rq);
 		double_rq_lock(src_rq, dst_rq);
@@ -2072,7 +2075,7 @@ static void dispatch_to_local_dsq_lock(struct rq *rq, struct rq_flags *rf,
 /**
  * dispatch_to_local_dsq_unlock - Undo dispatch_to_local_dsq_lock()
  * @rq: current rq which is locked
- * @rf: rq_flags to use when unlocking @rq
+ * @rf: optional rq_flags to use when unlocking @rq if its lock is pinned
  * @src_rq: rq to move task from
  * @dst_rq: rq to move task to
  *
@@ -2084,7 +2087,8 @@ static void dispatch_to_local_dsq_unlock(struct rq *rq, struct rq_flags *rf,
 	if (src_rq == dst_rq) {
 		raw_spin_rq_unlock(dst_rq);
 		raw_spin_rq_lock(rq);
-		rq_repin_lock(rq, rf);
+		if (rf)
+			rq_repin_lock(rq, rf);
 	} else if (rq == src_rq) {
 		double_unlock_balance(rq, dst_rq);
 	} else if (rq == dst_rq) {
@@ -2092,7 +2096,8 @@ static void dispatch_to_local_dsq_unlock(struct rq *rq, struct rq_flags *rf,
 	} else {
 		double_rq_unlock(src_rq, dst_rq);
 		raw_spin_rq_lock(rq);
-		rq_repin_lock(rq, rf);
+		if (rf)
+			rq_repin_lock(rq, rf);
 	}
 }
 #endif	/* CONFIG_SMP */
@@ -2214,7 +2219,7 @@ enum dispatch_to_local_dsq_ret {
 /**
  * dispatch_to_local_dsq - Dispatch a task to a local dsq
  * @rq: current rq which is locked
- * @rf: rq_flags to use when unlocking @rq
+ * @rf: optional rq_flags to use when unlocking @rq if its lock is pinned
  * @dsq_id: destination dsq ID
  * @p: task to dispatch
  * @enq_flags: %SCX_ENQ_*
-- 
2.45.2