It appears that the RPC/RDMA transport does not need serialization
of calls to its xpo_sendto method. Move the mutex into the socket
methods that still need that serialization.
Tail latencies are unambiguously better with this patch applied.
fio randrw 8KB 70/30 on NFSv3, smaller numbers are better:
clat percentiles (usec):
With xpt_mutex:
r | 99.99th=[ 8848]
w | 99.99th=[ 9634]
Without xpt_mutex:
r | 99.99th=[ 8586]
w | 99.99th=[ 8979]
Serializing the construction of RPC/RDMA transport headers is not
really necessary at this point, because the Linux NFS server
implementation never changes its credit grant on a connection. If
that should change, then svc_rdma_sendto will need to serialize
access to the transport's credit grant fields.
Reported-by: kbuild test robot <lkp@xxxxxxxxx>
[ cel: fix uninitialized variable warning ]
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
include/linux/sunrpc/svc_xprt.h | 6 +++++
net/sunrpc/svc_xprt.c | 12 ++--------
net/sunrpc/svcsock.c | 25 ++++++++++++++++++++
net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 35 +++++++++++++---------------
net/sunrpc/xprtrdma/svc_rdma_sendto.c | 10 +++-----
net/sunrpc/xprtsock.c | 12 ++++++++--
6 files changed, 64 insertions(+), 36 deletions(-)
diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index 9e1e046de176..aca35ab5cff2 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -117,6 +117,12 @@ static inline int register_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u
return 0;
}
+static inline bool svc_xprt_is_dead(const struct svc_xprt *xprt)
+{
+ return (test_bit(XPT_DEAD, &xprt->xpt_flags) != 0) ||
+ (test_bit(XPT_CLOSE, &xprt->xpt_flags) != 0);
+}
+
int svc_reg_xprt_class(struct svc_xprt_class *);
void svc_unreg_xprt_class(struct svc_xprt_class *);
void svc_xprt_init(struct net *, struct svc_xprt_class *, struct svc_xprt *,
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 2284ff038dad..07cdbf7d5764 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -914,16 +914,10 @@ int svc_send(struct svc_rqst *rqstp)
xb->page_len +
xb->tail[0].iov_len;
trace_svc_sendto(xb);
-
- /* Grab mutex to serialize outgoing data. */
- mutex_lock(&xprt->xpt_mutex);
trace_svc_stats_latency(rqstp);
- if (test_bit(XPT_DEAD, &xprt->xpt_flags)
- || test_bit(XPT_CLOSE, &xprt->xpt_flags))
- len = -ENOTCONN;
- else
- len = xprt->xpt_ops->xpo_sendto(rqstp);
- mutex_unlock(&xprt->xpt_mutex);
+
+ len = xprt->xpt_ops->xpo_sendto(rqstp);
+
trace_svc_send(rqstp, len);
svc_xprt_release(rqstp);
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 023514e392b3..3e7b6445e317 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -506,6 +506,9 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
* svc_udp_sendto - Send out a reply on a UDP socket
* @rqstp: completed svc_rqst
*
+ * xpt_mutex ensures @rqstp's whole message is written to the socket
+ * without interruption.
+ *
* Returns the number of bytes sent, or a negative errno.
*/
static int svc_udp_sendto(struct svc_rqst *rqstp)
@@ -531,6 +534,11 @@ static int svc_udp_sendto(struct svc_rqst *rqstp)
svc_set_cmsg_data(rqstp, cmh);
+ mutex_lock(&xprt->xpt_mutex);
+
+ if (svc_xprt_is_dead(xprt))
+ goto out_notconn;
+
err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, 0, &sent);
xdr_free_bvec(xdr);
if (err == -ECONNREFUSED) {
@@ -538,9 +546,15 @@ static int svc_udp_sendto(struct svc_rqst *rqstp)
err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, 0, &sent);
xdr_free_bvec(xdr);
}
+
+ mutex_unlock(&xprt->xpt_mutex);
if (err < 0)
return err;
return sent;
+
+out_notconn:
+ mutex_unlock(&xprt->xpt_mutex);
+ return -ENOTCONN;
}
static int svc_udp_has_wspace(struct svc_xprt *xprt)
@@ -1063,6 +1077,9 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
* svc_tcp_sendto - Send out a reply on a TCP socket
* @rqstp: completed svc_rqst
*
+ * xpt_mutex ensures @rqstp's whole message is written to the socket
+ * without interruption.
+ *
* Returns the number of bytes sent, or a negative errno.
*/
static int svc_tcp_sendto(struct svc_rqst *rqstp)
@@ -1080,12 +1097,19 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
svc_release_skb(rqstp);
+ mutex_lock(&xprt->xpt_mutex);
+ if (svc_xprt_is_dead(xprt))
+ goto out_notconn;
err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, marker, &sent);
xdr_free_bvec(xdr);
if (err < 0 || sent != (xdr->len + sizeof(marker)))
goto out_close;
+ mutex_unlock(&xprt->xpt_mutex);
return sent;
+out_notconn:
+ mutex_unlock(&xprt->xpt_mutex);
+ return -ENOTCONN;
out_close:
pr_notice("rpc-srv/tcp: %s: %s %d when sending %d bytes - shutting down socket\n",
xprt->xpt_server->sv_name,
@@ -1093,6 +1117,7 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
(err < 0) ? err : sent, xdr->len);
set_bit(XPT_CLOSE, &xprt->xpt_flags);
svc_xprt_enqueue(xprt);
+ mutex_unlock(&xprt->xpt_mutex);
return -EAGAIN;
}
diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
index af7eb8d202ae..d9aab4504f2c 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
@@ -210,34 +210,31 @@ rpcrdma_bc_send_request(struct svcxprt_rdma *rdma, struct rpc_rqst *rqst)
return -ENOTCONN;
}
-/* Send an RPC call on the passive end of a transport
- * connection.
+/**
+ * xprt_rdma_bc_send_request - Send a reverse-direction Call
+ * @rqst: rpc_rqst containing Call message to be sent
+ *
+ * Return values:
+ * %0 if the message was sent successfully
+ * %ENOTCONN if the message was not sent
*/
-static int
-xprt_rdma_bc_send_request(struct rpc_rqst *rqst)
+static int xprt_rdma_bc_send_request(struct rpc_rqst *rqst)
{
struct svc_xprt *sxprt = rqst->rq_xprt->bc_xprt;
- struct svcxprt_rdma *rdma;
+ struct svcxprt_rdma *rdma =
+ container_of(sxprt, struct svcxprt_rdma, sc_xprt);
int ret;
dprintk("svcrdma: sending bc call with xid: %08x\n",
be32_to_cpu(rqst->rq_xid));
- mutex_lock(&sxprt->xpt_mutex);
-
- ret = -ENOTCONN;
- rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
- if (!test_bit(XPT_DEAD, &sxprt->xpt_flags)) {
- ret = rpcrdma_bc_send_request(rdma, rqst);
- if (ret == -ENOTCONN)
- svc_close_xprt(sxprt);
- }
+ if (test_bit(XPT_DEAD, &sxprt->xpt_flags))
+ return -ENOTCONN;
- mutex_unlock(&sxprt->xpt_mutex);
-
- if (ret < 0)
- return ret;
- return 0;
+ ret = rpcrdma_bc_send_request(rdma, rqst);
+ if (ret == -ENOTCONN)
+ svc_close_xprt(sxprt);
+ return ret;
}
static void
diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index b6c8643867f2..38e7c3c8c4a9 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -868,12 +868,10 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
__be32 *p;
int ret;
- /* 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 = -ENOTCONN;
+ if (svc_xprt_is_dead(xprt))
+ goto err0;
+
ret = -ENOMEM;
sctxt = svc_rdma_send_ctxt_get(rdma);
if (!sctxt)
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 845d0be805ec..839c49330785 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -2548,8 +2548,16 @@ static int bc_sendto(struct rpc_rqst *req)
return sent;
}
-/*
- * The send routine. Borrows from svc_send
+/**
+ * bc_send_request - Send a backchannel Call on a TCP socket
+ * @req: rpc_rqst containing Call message to be sent
+ *
+ * xpt_mutex ensures @rqstp's whole message is written to the socket
+ * without interruption.
+ *
+ * Return values:
+ * %0 if the message was sent successfully
+ * %ENOTCONN if the message was not sent
*/
static int bc_send_request(struct rpc_rqst *req)
{
