RDS: Add flag for silent ops. Do atomic op before RDMA

Add a flag to the API so users can indicate they want
silent operations. This is needed because silent ops
cannot be used with USE_ONCE MRs, so we can't just
assume silent.

Also, change send_xmit to do atomic op before rdma op if
both are present, and centralize the hairy logic to determine if
we want to attempt silent, or not.

Signed-off-by: Andy Grover <andy.grover@oracle.com>

4 files changed, 36 insertions, 24 deletions

diff --git a/include/linux/rds.h b/include/linux/rds.h
index 9239152abf7a..109f1d343318 100644
--- a/include/linux/rds.h
+++ b/include/linux/rds.h
@@ -276,5 +276,6 @@ struct rds_rdma_notify {
 #define RDS_RDMA_USE_ONCE       0x0008  /* free MR after use */
 #define RDS_RDMA_DONTWAIT       0x0010  /* Don't wait in SET_BARRIER */
 #define RDS_RDMA_NOTIFY_ME      0x0020  /* Notify when operation completes */
+#define RDS_RDMA_SILENT         0x0040  /* Do not interrupt remote */
 
 #endif /* IB_RDS_H */
diff --git a/net/rds/rdma.c b/net/rds/rdma.c
index 5ba514684431..48781fe4431c 100644
--- a/net/rds/rdma.c
+++ b/net/rds/rdma.c
@@ -559,6 +559,7 @@ int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
         op->op_write = !!(args->flags & RDS_RDMA_READWRITE);
         op->op_fence = !!(args->flags & RDS_RDMA_FENCE);
         op->op_notify = !!(args->flags & RDS_RDMA_NOTIFY_ME);
+        op->op_silent = !!(args->flags & RDS_RDMA_SILENT);
         op->op_active = 1;
         op->op_recverr = rs->rs_recverr;
         WARN_ON(!nr_pages);
@@ -747,6 +748,7 @@ int rds_cmsg_atomic(struct rds_sock *rs, struct rds_message *rm,
         }
 
         rm->atomic.op_notify = !!(args->flags & RDS_RDMA_NOTIFY_ME);
+        rm->atomic.op_silent = !!(args->flags & RDS_RDMA_SILENT);
         rm->atomic.op_active = 1;
         rm->atomic.op_recverr = rs->rs_recverr;
         rm->atomic.op_sg = rds_message_alloc_sgs(rm, 1);
diff --git a/net/rds/rds.h b/net/rds/rds.h
index 46d190d08549..23b921000e74 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -319,6 +319,7 @@ struct rds_message {
                         unsigned int            op_notify:1;
                         unsigned int            op_recverr:1;
                         unsigned int            op_mapped:1;
+                        unsigned int            op_silent:1;
                         unsigned int            op_active:1;
                         struct scatterlist      *op_sg;
                         struct rds_notifier     *op_notifier;
@@ -333,6 +334,7 @@ struct rds_message {
                         unsigned int            op_notify:1;
                         unsigned int            op_recverr:1;
                         unsigned int            op_mapped:1;
+                        unsigned int            op_silent:1;
                         unsigned int            op_active:1;
                         unsigned int            op_bytes;
                         unsigned int            op_nents;
diff --git a/net/rds/send.c b/net/rds/send.c
index cdca9747fcbc..38567f3ee7e8 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -250,42 +250,50 @@ int rds_send_xmit(struct rds_connection *conn)
                         conn->c_xmit_rm = rm;
                 }
 
-                if (rm->atomic.op_active && !conn->c_xmit_atomic_sent) {
-                        ret = conn->c_trans->xmit_atomic(conn, rm);
+                /* The transport either sends the whole rdma or none of it */
+                if (rm->rdma.op_active && !conn->c_xmit_rdma_sent) {
+                        ret = conn->c_trans->xmit_rdma(conn, &rm->rdma);
                         if (ret)
                                 break;
-                        conn->c_xmit_atomic_sent = 1;
+                        conn->c_xmit_rdma_sent = 1;
+
                         /* The transport owns the mapped memory for now.
                          * You can't unmap it while it's on the send queue */
                         set_bit(RDS_MSG_MAPPED, &rm->m_flags);
-
-                        /*
-                         * This is evil, muahaha.
-                         * We permit 0-byte sends. (rds-ping depends on this.)
-                         * BUT if there is an atomic op and no sent data,
-                         * we turn off sending the header, to achieve
-                         * "silent" atomics.
-                         * But see below; RDMA op might toggle this back on!
-                         */
-                        if (rm->data.op_nents == 0)
-                                rm->data.op_active = 0;
                 }
 
-                /* The transport either sends the whole rdma or none of it */
-                if (rm->rdma.op_active && !conn->c_xmit_rdma_sent) {
-                        ret = conn->c_trans->xmit_rdma(conn, &rm->rdma);
+                if (rm->atomic.op_active && !conn->c_xmit_atomic_sent) {
+                        ret = conn->c_trans->xmit_atomic(conn, rm);
                         if (ret)
                                 break;
-                        conn->c_xmit_rdma_sent = 1;
-
-                        /* rdmas need data sent, even if just the header */
-                        rm->data.op_active = 1;
-
+                        conn->c_xmit_atomic_sent = 1;
                         /* The transport owns the mapped memory for now.
                          * You can't unmap it while it's on the send queue */
                         set_bit(RDS_MSG_MAPPED, &rm->m_flags);
                 }
 
+                /*
+                 * A number of cases require an RDS header to be sent
+                 * even if there is no data.
+                 * We permit 0-byte sends; rds-ping depends on this.
+                 * However, if there are exclusively attached silent ops,
+                 * we skip the hdr/data send, to enable silent operation.
+                 */
+                if (rm->data.op_nents == 0) {
+                        int ops_present;
+                        int all_ops_are_silent = 1;
+
+                        ops_present = (rm->atomic.op_active || rm->rdma.op_active);
+                        if (rm->atomic.op_active && !rm->atomic.op_silent)
+                                all_ops_are_silent = 0;
+                        if (rm->rdma.op_active && !rm->rdma.op_silent)
+                                all_ops_are_silent = 0;
+
+                        if (ops_present && all_ops_are_silent
+                            && !rm->m_rdma_cookie)
+                                rm->data.op_active = 0;
+                }
+
                 if (rm->data.op_active && !conn->c_xmit_data_sent) {
                         ret = conn->c_trans->xmit(conn, rm,
                                                   conn->c_xmit_hdr_off,
@@ -1009,8 +1017,7 @@ int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
         if (ret)
                 goto out;
 
-        if ((rm->m_rdma_cookie || rm->rdma.op_active) &&
-            !conn->c_trans->xmit_rdma) {
+        if (rm->rdma.op_active && !conn->c_trans->xmit_rdma) {
                 if (printk_ratelimit())
                         printk(KERN_NOTICE "rdma_op %p conn xmit_rdma %p\n",
                                &rm->rdma, conn->c_trans->xmit_rdma);