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svcrdma: Relieve contention on sc_send_lock.

Browse source 
/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@oracle.com>
Reviewed-By: Tom Talpey <tom@talpey.com>
This commit is contained in:
Chuck Lever 2021-02-09 10:32:20 -05:00
parent 6c8c84f525
commit b6c2bfea09
3 changed files with 11 additions and 18 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
include/linux/sunrpc/svc_rdma.h
View file

@ -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;

23
net/sunrpc/xprtrdma/svc_rdma_sendto.c
View file

@ -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);
}
/**

2
net/sunrpc/xprtrdma/svc_rdma_transport.c
View file

@ -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);