From: Chuck Lever Date: Fri, 5 Jun 2026 20:40:33 +0000 (-0400) Subject: xprtrdma: Convert send buffer free list to llist X-Git-Url: http://git.ipfire.org/index.cgi?a=commitdiff_plain;h=417efc520207615df1083567f674085be697b845;p=thirdparty%2Fkernel%2Flinux.git xprtrdma: Convert send buffer free list to llist rpcrdma_buffer_get() and rpcrdma_buffer_put() both take rb_lock to pop/push from the rb_send_bufs free list. Under high I/O concurrency (e.g., nconnect=N with small random writes), this spinlock is contended between the request submission path and the transport completion path. Replace the list_head with an llist_head. The put side uses lockless llist_add(), which is safe for concurrent producers. The get side retains the spinlock to satisfy the llist single-consumer contract portably; submitters continue to serialize there. Completion handlers returning buffers no longer contend on rb_lock, eliminating contention on the return path. rb_lock remains for the MR free list and the tracking lists used during setup and teardown. rb_free_reps already uses llist_head, so the llist idiom is established in this structure. The precedent is the data structure, not the locking: rb_free_reps serializes its single consumer through the re_receiving gate in rpcrdma_post_recvs, whereas rb_send_bufs serializes its consumer with rb_lock. Both satisfy the llist single-consumer contract. Signed-off-by: Chuck Lever Signed-off-by: Anna Schumaker --- diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c index 92c691d2521f0..993bc5c444a4b 100644 --- a/net/sunrpc/xprtrdma/verbs.c +++ b/net/sunrpc/xprtrdma/verbs.c @@ -1120,7 +1120,7 @@ int rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt) INIT_LIST_HEAD(&buf->rb_all_mrs); INIT_WORK(&buf->rb_refresh_worker, rpcrdma_mr_refresh_worker); - INIT_LIST_HEAD(&buf->rb_send_bufs); + init_llist_head(&buf->rb_send_bufs); INIT_LIST_HEAD(&buf->rb_allreqs); INIT_LIST_HEAD(&buf->rb_all_reps); @@ -1134,7 +1134,7 @@ int rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt) RPCRDMA_V1_DEF_INLINE_SIZE * 2); if (!req) goto out; - list_add(&req->rl_list, &buf->rb_send_bufs); + llist_add(&req->rl_node, &buf->rb_send_bufs); } init_llist_head(&buf->rb_free_reps); @@ -1214,16 +1214,14 @@ static void rpcrdma_mrs_destroy(struct rpcrdma_xprt *r_xprt) void rpcrdma_buffer_destroy(struct rpcrdma_buffer *buf) { - rpcrdma_reps_destroy(buf); + struct rpcrdma_req *req, *next; + struct llist_node *node; - while (!list_empty(&buf->rb_send_bufs)) { - struct rpcrdma_req *req; + rpcrdma_reps_destroy(buf); - req = list_first_entry(&buf->rb_send_bufs, - struct rpcrdma_req, rl_list); - list_del(&req->rl_list); + node = llist_del_all(&buf->rb_send_bufs); + llist_for_each_entry_safe(req, next, node, rl_node) rpcrdma_req_destroy(req); - } } /** @@ -1270,15 +1268,15 @@ void rpcrdma_reply_put(struct rpcrdma_buffer *buffers, struct rpcrdma_req *req) struct rpcrdma_req * rpcrdma_buffer_get(struct rpcrdma_buffer *buffers) { - struct rpcrdma_req *req; + struct llist_node *node; + /* Calls to llist_del_first are required to be serialized */ spin_lock(&buffers->rb_lock); - req = list_first_entry_or_null(&buffers->rb_send_bufs, - struct rpcrdma_req, rl_list); - if (req) - list_del_init(&req->rl_list); + node = llist_del_first(&buffers->rb_send_bufs); spin_unlock(&buffers->rb_lock); - return req; + if (!node) + return NULL; + return llist_entry(node, struct rpcrdma_req, rl_node); } /** @@ -1291,9 +1289,7 @@ void rpcrdma_buffer_put(struct rpcrdma_buffer *buffers, struct rpcrdma_req *req) { rpcrdma_reply_put(buffers, req); - spin_lock(&buffers->rb_lock); - list_add(&req->rl_list, &buffers->rb_send_bufs); - spin_unlock(&buffers->rb_lock); + llist_add(&req->rl_node, &buffers->rb_send_bufs); } /* Returns a pointer to a rpcrdma_regbuf object, or NULL. diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h index f879d9b9f57ef..ae036719f840c 100644 --- a/net/sunrpc/xprtrdma/xprt_rdma.h +++ b/net/sunrpc/xprtrdma/xprt_rdma.h @@ -332,7 +332,7 @@ enum { struct rpcrdma_buffer; struct rpcrdma_req { - struct list_head rl_list; + struct llist_node rl_node; struct rpc_rqst rl_slot; struct rpcrdma_rep *rl_reply; struct xdr_stream rl_stream; @@ -374,14 +374,14 @@ rpcrdma_mr_pop(struct list_head *list) } /* - * struct rpcrdma_buffer -- holds list/queue of pre-registered memory for - * inline requests/replies, and client/server credits. + * struct rpcrdma_buffer -- holds pre-registered memory for inline + * requests/replies, and client/server credits. * * One of these is associated with a transport instance */ struct rpcrdma_buffer { spinlock_t rb_lock; - struct list_head rb_send_bufs; + struct llist_head rb_send_bufs; struct list_head rb_mrs; unsigned long rb_sc_head;