From: Gerd Rausch <[email protected]> Instead of just blocking the sender until "c_npaths" is known (it gets updated upon the receipt of a MPRDS PONG message), simply use the first lane (cp_index#0).
But just using the first lane isn't enough. As soon as we enqueue messages on a different lane, we'd run the risk of out-of-order delivery of RDS messages. Earlier messages enqueued on "cp_index == 0" could be delivered later than more recent messages enqueued on "cp_index > 0", mostly because of possible head of line blocking issues causing the first lane to be slower. To avoid that, we simply take a snapshot of "cp_next_tx_seq" at the time we're about to fan-out to more lanes. Then we delay the transmission of messages enqueued on other lanes with "cp_index > 0" until cp_index#0 caught up with the delivery of new messages (from "cp_send_queue") as well as in-flight messages (from "cp_retrans") that haven't been acknowledged yet by the receiver. We also add a new counter "mprds_catchup_tx0_retries" to keep track of how many times "rds_send_xmit" had to suspend activities, because it was waiting for the first lane to catch up. Signed-off-by: Gerd Rausch <[email protected]> Signed-off-by: Allison Henderson <[email protected]> --- net/rds/rds.h | 3 ++ net/rds/recv.c | 23 +++++++++-- net/rds/send.c | 102 +++++++++++++++++++++++++++++++----------------- net/rds/stats.c | 1 + 4 files changed, 90 insertions(+), 39 deletions(-) diff --git a/net/rds/rds.h b/net/rds/rds.h index d942057b91ee..f78477912e7c 100644 --- a/net/rds/rds.h +++ b/net/rds/rds.h @@ -170,6 +170,8 @@ struct rds_connection { u32 c_my_gen_num; u32 c_peer_gen_num; + + u64 c_cp0_mprds_catchup_tx_seq; }; static inline @@ -748,6 +750,7 @@ struct rds_statistics { uint64_t s_recv_bytes_added_to_socket; uint64_t s_recv_bytes_removed_from_socket; uint64_t s_send_stuck_rm; + uint64_t s_mprds_catchup_tx0_retries; }; /* af_rds.c */ diff --git a/net/rds/recv.c b/net/rds/recv.c index ddf128a02347..889a5b7935e5 100644 --- a/net/rds/recv.c +++ b/net/rds/recv.c @@ -208,6 +208,9 @@ static void rds_recv_hs_exthdrs(struct rds_header *hdr, } buffer; bool new_with_sport_idx = false; u32 new_peer_gen_num = 0; + int new_npaths; + + new_npaths = conn->c_npaths; while (1) { len = sizeof(buffer); @@ -217,8 +220,8 @@ static void rds_recv_hs_exthdrs(struct rds_header *hdr, /* Process extension header here */ switch (type) { case RDS_EXTHDR_NPATHS: - conn->c_npaths = min_t(int, RDS_MPATH_WORKERS, - be16_to_cpu(buffer.rds_npaths)); + new_npaths = min_t(int, RDS_MPATH_WORKERS, + be16_to_cpu(buffer.rds_npaths)); break; case RDS_EXTHDR_GEN_NUM: new_peer_gen_num = be32_to_cpu(buffer.rds_gen_num); @@ -233,8 +236,22 @@ static void rds_recv_hs_exthdrs(struct rds_header *hdr, } conn->c_with_sport_idx = new_with_sport_idx; + + if (new_npaths > 1 && new_npaths != conn->c_npaths) { + /* We're about to fan-out. + * Make sure that messages from cp_index#0 + * are sent prior to handling other lanes. + */ + struct rds_conn_path *cp0 = conn->c_path; + unsigned long flags; + + spin_lock_irqsave(&cp0->cp_lock, flags); + conn->c_cp0_mprds_catchup_tx_seq = cp0->cp_next_tx_seq; + spin_unlock_irqrestore(&cp0->cp_lock, flags); + } /* if RDS_EXTHDR_NPATHS was not found, default to a single-path */ - conn->c_npaths = max_t(int, conn->c_npaths, 1); + conn->c_npaths = max_t(int, new_npaths, 1); + conn->c_ping_triggered = 0; rds_conn_peer_gen_update(conn, new_peer_gen_num); diff --git a/net/rds/send.c b/net/rds/send.c index 85e1c5352ad8..599c2cfb7a1d 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -119,6 +119,57 @@ static void release_in_xmit(struct rds_conn_path *cp) wake_up_all(&cp->cp_waitq); } +/* + * Helper function for multipath fanout to ensure lane 0 transmits queued + * messages before other lanes to prevent out-of-order delivery. + * + * Returns true if lane 0 still has messages or false otherwise + */ +static bool rds_mprds_cp0_catchup(struct rds_connection *conn) +{ + struct rds_conn_path *cp0 = conn->c_path; + struct rds_message *rm0; + unsigned long flags; + bool ret = false; + + spin_lock_irqsave(&cp0->cp_lock, flags); + + /* the oldest / first message in the retransmit queue + * has to be at or beyond c_cp0_mprds_catchup_tx_seq + */ + if (!list_empty(&cp0->cp_retrans)) { + rm0 = list_entry(cp0->cp_retrans.next, struct rds_message, + m_conn_item); + if (be64_to_cpu(rm0->m_inc.i_hdr.h_sequence) < + conn->c_cp0_mprds_catchup_tx_seq) { + /* the retransmit queue of cp_index#0 has not + * quite caught up yet + */ + ret = true; + goto unlock; + } + } + + /* the oldest / first message of the send queue + * has to be at or beyond c_cp0_mprds_catchup_tx_seq + */ + rm0 = cp0->cp_xmit_rm; + if (!rm0 && !list_empty(&cp0->cp_send_queue)) + rm0 = list_entry(cp0->cp_send_queue.next, struct rds_message, + m_conn_item); + if (rm0 && be64_to_cpu(rm0->m_inc.i_hdr.h_sequence) < + conn->c_cp0_mprds_catchup_tx_seq) { + /* the send queue of cp_index#0 has not quite + * caught up yet + */ + ret = true; + } + +unlock: + spin_unlock_irqrestore(&cp0->cp_lock, flags); + return ret; +} + /* * We're making the conscious trade-off here to only send one message * down the connection at a time. @@ -248,6 +299,14 @@ int rds_send_xmit(struct rds_conn_path *cp) if (batch_count >= send_batch_count) goto over_batch; + /* make sure cp_index#0 caught up during fan-out in + * order to avoid lane races + */ + if (cp->cp_index > 0 && rds_mprds_cp0_catchup(conn)) { + rds_stats_inc(s_mprds_catchup_tx0_retries); + goto over_batch; + } + spin_lock_irqsave(&cp->cp_lock, flags); if (!list_empty(&cp->cp_send_queue)) { @@ -1042,39 +1101,6 @@ static int rds_cmsg_send(struct rds_sock *rs, struct rds_message *rm, return ret; } -static int rds_send_mprds_hash(struct rds_sock *rs, - struct rds_connection *conn, int nonblock) -{ - int hash; - - if (conn->c_npaths == 0) - hash = RDS_MPATH_HASH(rs, RDS_MPATH_WORKERS); - else - hash = RDS_MPATH_HASH(rs, conn->c_npaths); - if (conn->c_npaths == 0 && hash != 0) { - rds_send_ping(conn, 0); - - /* The underlying connection is not up yet. Need to wait - * until it is up to be sure that the non-zero c_path can be - * used. But if we are interrupted, we have to use the zero - * c_path in case the connection ends up being non-MP capable. - */ - if (conn->c_npaths == 0) { - /* Cannot wait for the connection be made, so just use - * the base c_path. - */ - if (nonblock) - return 0; - if (wait_event_interruptible(conn->c_hs_waitq, - conn->c_npaths != 0)) - hash = 0; - } - if (conn->c_npaths == 1) - hash = 0; - } - return hash; -} - static int rds_rdma_bytes(struct msghdr *msg, size_t *rdma_bytes) { struct rds_rdma_args *args; @@ -1304,10 +1330,14 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len) rs->rs_conn = conn; } - if (conn->c_trans->t_mp_capable) - cpath = &conn->c_path[rds_send_mprds_hash(rs, conn, nonblock)]; - else + if (conn->c_trans->t_mp_capable) { + /* Use c_path[0] until we learn that + * the peer supports more (c_npaths > 1) + */ + cpath = &conn->c_path[RDS_MPATH_HASH(rs, conn->c_npaths ? : 1)]; + } else { cpath = &conn->c_path[0]; + } rm->m_conn_path = cpath; diff --git a/net/rds/stats.c b/net/rds/stats.c index cb2e3d2cdf73..24ee22d09e8c 100644 --- a/net/rds/stats.c +++ b/net/rds/stats.c @@ -79,6 +79,7 @@ static const char *const rds_stat_names[] = { "recv_bytes_added_to_sock", "recv_bytes_freed_fromsock", "send_stuck_rm", + "mprds_catchup_tx0_retries", }; void rds_stats_info_copy(struct rds_info_iterator *iter, -- 2.43.0
