SUNRPC: add list of idle threads

Rather than searching a list of threads to find an idle one, having a
list of idle threads allows an idle thread to be found immediately.

This adds some spin_lock calls which is not ideal, but as the hold-time
is tiny it is still faster than searching a list.  A future patch will
remove them using llist.h.  This involves some subtlety and so is left
to a separate patch.

This removes the need for the RQ_BUSY flag.  The rqst is "busy"
precisely when it is not on the "idle" list.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index db579bbc0a0a..9d080fe2dcdf 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -510,6 +510,7 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
 		pool->sp_id = i;
 		INIT_LIST_HEAD(&pool->sp_sockets);
 		INIT_LIST_HEAD(&pool->sp_all_threads);
+		INIT_LIST_HEAD(&pool->sp_idle_threads);
 		spin_lock_init(&pool->sp_lock);
 
 		percpu_counter_init(&pool->sp_messages_arrived, 0, GFP_KERNEL);
@@ -641,7 +642,7 @@ svc_rqst_alloc(struct svc_serv *serv, struct svc_pool *pool, int node)
 
 	folio_batch_init(&rqstp->rq_fbatch);
 
-	__set_bit(RQ_BUSY, &rqstp->rq_flags);
+	svc_thread_set_busy(rqstp);
 	rqstp->rq_server = serv;
 	rqstp->rq_pool = pool;
 
@@ -702,10 +703,13 @@ void svc_pool_wake_idle_thread(struct svc_pool *pool)
 	struct svc_rqst	*rqstp;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(rqstp, &pool->sp_all_threads, rq_all) {
-		if (test_and_set_bit(RQ_BUSY, &rqstp->rq_flags))
-			continue;
-
+	spin_lock_bh(&pool->sp_lock);
+	rqstp = list_first_entry_or_null(&pool->sp_idle_threads,
+					 struct svc_rqst, rq_idle);
+	if (rqstp)
+		list_del_init(&rqstp->rq_idle);
+	spin_unlock_bh(&pool->sp_lock);
+	if (rqstp) {
 		WRITE_ONCE(rqstp->rq_qtime, ktime_get());
 		wake_up_process(rqstp->rq_task);
 		rcu_read_unlock();