/proc/lock_stat indicates the the sc_send_lock is heavily
contended when the server is under load from a single client.
To address this, convert the send_ctxt free list to an llist.
Returning an item to the send_ctxt cache is now waitless, which
reduces the instruction path length in the single-threaded Send
handler (svc_rdma_wc_send).
The goal is to enable the ib_comp_wq worker to handle a higher
RPC/RDMA Send completion rate given the same CPU resources. This
change reduces CPU utilization of Send completion by 2-3% on my
server.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
include/linux/sunrpc/svc_rdma.h | 4 ++--
net/sunrpc/xprtrdma/svc_rdma_sendto.c | 23 ++++++++---------------
net/sunrpc/xprtrdma/svc_rdma_transport.c | 2 +-
3 files changed, 11 insertions(+), 18 deletions(-)
diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index 57c60ffe76dd..5f8d5af6556c 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -90,7 +90,7 @@ struct svcxprt_rdma {
struct ib_pd *sc_pd;
spinlock_t sc_send_lock;
- struct list_head sc_send_ctxts;
+ struct llist_head sc_send_ctxts;
spinlock_t sc_rw_ctxt_lock;
struct list_head sc_rw_ctxts;
@@ -150,7 +150,7 @@ struct svc_rdma_recv_ctxt {
};
struct svc_rdma_send_ctxt {
- struct list_head sc_list;
+ struct llist_node sc_node;
struct rpc_rdma_cid sc_cid;
struct ib_send_wr sc_send_wr;
diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index fba2ee4eb607..599021b2391d 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -113,13 +113,6 @@
static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc);
-static inline struct svc_rdma_send_ctxt *
-svc_rdma_next_send_ctxt(struct list_head *list)
-{
- return list_first_entry_or_null(list, struct svc_rdma_send_ctxt,
- sc_list);
-}
-
static void svc_rdma_send_cid_init(struct svcxprt_rdma *rdma,
struct rpc_rdma_cid *cid)
{
@@ -182,9 +175,10 @@ svc_rdma_send_ctxt_alloc(struct svcxprt_rdma *rdma)
void svc_rdma_send_ctxts_destroy(struct svcxprt_rdma *rdma)
{
struct svc_rdma_send_ctxt *ctxt;
+ struct llist_node *node;
- while ((ctxt = svc_rdma_next_send_ctxt(&rdma->sc_send_ctxts))) {
- list_del(&ctxt->sc_list);
+ while ((node = llist_del_first(&rdma->sc_send_ctxts)) != NULL) {
+ ctxt = llist_entry(node, struct svc_rdma_send_ctxt, sc_node);
ib_dma_unmap_single(rdma->sc_pd->device,
ctxt->sc_sges[0].addr,
rdma->sc_max_req_size,
@@ -204,12 +198,13 @@ void svc_rdma_send_ctxts_destroy(struct svcxprt_rdma *rdma)
struct svc_rdma_send_ctxt *svc_rdma_send_ctxt_get(struct svcxprt_rdma *rdma)
{
struct svc_rdma_send_ctxt *ctxt;
+ struct llist_node *node;
spin_lock(&rdma->sc_send_lock);
- ctxt = svc_rdma_next_send_ctxt(&rdma->sc_send_ctxts);
- if (!ctxt)
+ node = llist_del_first(&rdma->sc_send_ctxts);
+ if (!node)
goto out_empty;
- list_del(&ctxt->sc_list);
+ ctxt = llist_entry(node, struct svc_rdma_send_ctxt, sc_node);
spin_unlock(&rdma->sc_send_lock);
out:
@@ -253,9 +248,7 @@ void svc_rdma_send_ctxt_put(struct svcxprt_rdma *rdma,
ctxt->sc_sges[i].length);
}
- spin_lock(&rdma->sc_send_lock);
- list_add(&ctxt->sc_list, &rdma->sc_send_ctxts);
- spin_unlock(&rdma->sc_send_lock);
+ llist_add(&ctxt->sc_node, &rdma->sc_send_ctxts);
}
/**
diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
index d94b7759ada1..99474078c304 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -136,7 +136,7 @@ static struct svcxprt_rdma *svc_rdma_create_xprt(struct svc_serv *serv,
svc_xprt_init(net, &svc_rdma_class, &cma_xprt->sc_xprt, serv);
INIT_LIST_HEAD(&cma_xprt->sc_accept_q);
INIT_LIST_HEAD(&cma_xprt->sc_rq_dto_q);
- INIT_LIST_HEAD(&cma_xprt->sc_send_ctxts);
+ init_llist_head(&cma_xprt->sc_send_ctxts);
init_llist_head(&cma_xprt->sc_recv_ctxts);
INIT_LIST_HEAD(&cma_xprt->sc_rw_ctxts);
init_waitqueue_head(&cma_xprt->sc_send_wait);
