[PATCH RFC 1/3] SUNRPC: add a second per-pool ready queue for high-priority transports

A pool's ready transports are tracked in a single lockless queue,
sp_xprts, and dispatched in FIFO order.  A transport's position in that
queue is independent of how much work it already has in flight, so a
connection that keeps many requests pending is serviced on equal terms
with one that has been idle -- the idle flow's next request waits behind
the busy flow's backlog.

Add a second queue, sp_xprts_hi, alongside sp_xprts and initialise it
with each pool.  Nothing is enqueued to it yet, so this is no functional
change; a later patch routes transports with no requests in flight onto
it and drains it ahead of sp_xprts, giving an idle flow's request a
latency floor that a backlogged flow cannot push it below.

Signed-off-by: Benjamin Coddington <bcodding-F/[email protected]>
---
 include/linux/sunrpc/svc.h | 1 +
 net/sunrpc/svc.c           | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 3a0152d926fb..89fa90f6d360 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -39,6 +39,7 @@ struct svc_pool {
 	unsigned int		sp_nrthrmin;	/* Min number of threads to run per pool */
 	unsigned int		sp_nrthrmax;	/* Max requested number of threads in pool */
 	struct lwq		sp_xprts;	/* pending transports */
+	struct lwq		sp_xprts_hi;	/* high-priority pending transports */
 	struct list_head	sp_all_threads;	/* all server threads */
 	struct llist_head	sp_idle_threads; /* idle server threads */
 
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index dd80a2eaaa74..7ead2db314c7 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -566,6 +566,7 @@ __svc_create(struct svc_program *prog, int nprogs, struct svc_stat *stats,
 
 		pool->sp_id = i;
 		lwq_init(&pool->sp_xprts);
+		lwq_init(&pool->sp_xprts_hi);
 		INIT_LIST_HEAD(&pool->sp_all_threads);
 		init_llist_head(&pool->sp_idle_threads);
 
-- 
2.53.0