From e4eb42cecc6dc546aac888ee4913d59121e886ee Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Tue, 29 Nov 2016 11:04:50 -0500 Subject: svcrdma: Remove BH-disabled spin locking in svc_rdma_send() svcrdma's current SQ accounting algorithm takes sc_lock and disables bottom-halves while posting all RDMA Read, Write, and Send WRs. This is relatively heavyweight serialization. And note that Write and Send are already fully serialized by the xpt_mutex. Using a single atomic_t should be all that is necessary to guarantee that ib_post_send() is called only when there is enough space on the send queue. This is what the other RDMA-enabled storage targets do. Signed-off-by: Chuck Lever Signed-off-by: J. Bruce Fields --- net/sunrpc/xprtrdma/svc_rdma_sendto.c | 7 ++++++- net/sunrpc/xprtrdma/svc_rdma_transport.c | 25 ++++++++++--------------- 2 files changed, 16 insertions(+), 16 deletions(-) (limited to 'net/sunrpc') diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c index 0a58d4062f2f..30eeab527bd0 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c @@ -594,7 +594,12 @@ int svc_rdma_sendto(struct svc_rqst *rqstp) goto err0; inline_bytes = rqstp->rq_res.len; - /* Create the RDMA response header */ + /* Create the RDMA response header. xprt->xpt_mutex, + * acquired in svc_send(), serializes RPC replies. The + * code path below that inserts the credit grant value + * into each transport header runs only inside this + * critical section. + */ ret = -ENOMEM; res_page = alloc_page(GFP_KERNEL); if (!res_page) diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c index 6864fb967038..da990d7f8b20 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c @@ -434,7 +434,7 @@ static void svc_rdma_send_wc_common(struct svcxprt_rdma *xprt, goto err; out: - atomic_dec(&xprt->sc_sq_count); + atomic_inc(&xprt->sc_sq_avail); wake_up(&xprt->sc_send_wait); return; @@ -1008,6 +1008,7 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt) newxprt->sc_rq_depth = newxprt->sc_max_requests + newxprt->sc_max_bc_requests; newxprt->sc_sq_depth = RPCRDMA_SQ_DEPTH_MULT * newxprt->sc_rq_depth; + atomic_set(&newxprt->sc_sq_avail, newxprt->sc_sq_depth); if (!svc_rdma_prealloc_ctxts(newxprt)) goto errout; @@ -1333,15 +1334,13 @@ int svc_rdma_send(struct svcxprt_rdma *xprt, struct ib_send_wr *wr) /* If the SQ is full, wait until an SQ entry is available */ while (1) { - spin_lock_bh(&xprt->sc_lock); - if (xprt->sc_sq_depth < atomic_read(&xprt->sc_sq_count) + wr_count) { - spin_unlock_bh(&xprt->sc_lock); + if ((atomic_sub_return(wr_count, &xprt->sc_sq_avail) < 0)) { atomic_inc(&rdma_stat_sq_starve); /* Wait until SQ WR available if SQ still full */ + atomic_add(wr_count, &xprt->sc_sq_avail); wait_event(xprt->sc_send_wait, - atomic_read(&xprt->sc_sq_count) < - xprt->sc_sq_depth); + atomic_read(&xprt->sc_sq_avail) > wr_count); if (test_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags)) return -ENOTCONN; continue; @@ -1351,21 +1350,17 @@ int svc_rdma_send(struct svcxprt_rdma *xprt, struct ib_send_wr *wr) svc_xprt_get(&xprt->sc_xprt); /* Bump used SQ WR count and post */ - atomic_add(wr_count, &xprt->sc_sq_count); ret = ib_post_send(xprt->sc_qp, wr, &bad_wr); if (ret) { set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags); - atomic_sub(wr_count, &xprt->sc_sq_count); for (i = 0; i < wr_count; i ++) svc_xprt_put(&xprt->sc_xprt); - dprintk("svcrdma: failed to post SQ WR rc=%d, " - "sc_sq_count=%d, sc_sq_depth=%d\n", - ret, atomic_read(&xprt->sc_sq_count), - xprt->sc_sq_depth); - } - spin_unlock_bh(&xprt->sc_lock); - if (ret) + dprintk("svcrdma: failed to post SQ WR rc=%d\n", ret); + dprintk(" sc_sq_avail=%d, sc_sq_depth=%d\n", + atomic_read(&xprt->sc_sq_avail), + xprt->sc_sq_depth); wake_up(&xprt->sc_send_wait); + } break; } return ret; -- cgit v1.2.3