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authorChuck Lever <chuck.lever@oracle.com>2016-11-29 11:04:50 -0500
committerJ. Bruce Fields <bfields@redhat.com>2016-11-30 17:31:13 -0500
commite4eb42cecc6dc546aac888ee4913d59121e886ee (patch)
treed78a0e21882dfb0ba3046a6f6962285d3efac9ef /net/sunrpc/xprtrdma
parent5fdca6531434c1c1b2d584873afdda52e5ad448c (diff)
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 <chuck.lever@oracle.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net/sunrpc/xprtrdma')
-rw-r--r--net/sunrpc/xprtrdma/svc_rdma_sendto.c7
-rw-r--r--net/sunrpc/xprtrdma/svc_rdma_transport.c25
2 files changed, 16 insertions, 16 deletions
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;