rxrpc: Implement slow-start
Implement RxRPC slow-start, which is similar to RFC 5681 for TCP. A
tracepoint is added to log the state of the congestion management algorithm
and the decisions it makes.
Notes:
(1) Since we send fixed-size DATA packets (apart from the final packet in
each phase), counters and calculations are in terms of packets rather
than bytes.
(2) The ACK packet carries the equivalent of TCP SACK.
(3) The FLIGHT_SIZE calculation in RFC 5681 doesn't seem particularly
suited to SACK of a small number of packets. It seems that, almost
inevitably, by the time three 'duplicate' ACKs have been seen, we have
narrowed the loss down to one or two missing packets, and the
FLIGHT_SIZE calculation ends up as 2.
(4) In rxrpc_resend(), if there was no data that apparently needed
retransmission, we transmit a PING ACK to ask the peer to tell us what
its Rx window state is.
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index a53f4c2..d4b3293 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -160,6 +160,14 @@
call->rx_winsize = rxrpc_rx_window_size;
call->tx_winsize = 16;
call->rx_expect_next = 1;
+
+ if (RXRPC_TX_SMSS > 2190)
+ call->cong_cwnd = 2;
+ else if (RXRPC_TX_SMSS > 1095)
+ call->cong_cwnd = 3;
+ else
+ call->cong_cwnd = 4;
+ call->cong_ssthresh = RXRPC_RXTX_BUFF_SIZE - 1;
return call;
nomem_2:
@@ -176,6 +184,7 @@
gfp_t gfp)
{
struct rxrpc_call *call;
+ ktime_t now;
_enter("");
@@ -185,6 +194,9 @@
call->state = RXRPC_CALL_CLIENT_AWAIT_CONN;
call->service_id = srx->srx_service;
call->tx_phase = true;
+ now = ktime_get_real();
+ call->acks_latest_ts = now;
+ call->cong_tstamp = now;
_leave(" = %p", call);
return call;
@@ -325,6 +337,7 @@
call->state = RXRPC_CALL_SERVER_ACCEPTING;
if (sp->hdr.securityIndex > 0)
call->state = RXRPC_CALL_SERVER_SECURING;
+ call->cong_tstamp = skb->tstamp;
/* Set the channel for this call. We don't get channel_lock as we're
* only defending against the data_ready handler (which we're called
