I am resending this since I have checked this against possible cases and fixed
the following cases:
* the packet size `s' has to be seeded when the first packet is sent, since
several calculations later depend on `s'
This is now done, and an analysis has been added that this is safe.
* It is perfectly ok and not a bug condition for a receiver to receive packets
with a zero packet size. I have therefore removed the BUG_ON conditions and
replaced them with ccid3_pr_debug messages - these can be switched off at will
* has been uploaded to replace the previous version on
http://www.erg.abdn.ac.uk/users/gerrit/dccp/patch-backlog/12e_CCID3_packet_size_EWMA.diff
--------------> Commit message <------------------------------------------------------
[CCID 3]: Track RX/TX packet size `s' using moving-average
Problem:
--------
Currently, the receiver/sender packet size `s' of the TCP throughput
equation [RFC 3448, 3.1] has to be communicated manually via socket options
to the CCID 3 module. This has been discussed on dccp@vger, see e.g.
http://www.mail-archive.com/dccp@xxxxxxxxxxxxxxx/msg00582.html
Solution
--------
This patch implements automatically tracking the packet size `s', for receiver and
sender. Socket options to commmunicate the packet size are then no longer needed.
It implements the strategy presented on
http://www.mail-archive.com/dccp@xxxxxxxxxxxxxxx/msg00581.html
Assumptions:
------------
Several other bits of code rely on the value of `s' being set. This patch has been verified to
ensure that `s' is not unset (i.e. 0) when other functions try to use it:
* ccid3_hc_tx_send_packet only sends packets with a payload size > 0
* the `s' value is seeded upon first sending (state NO_SENT)
* the functions which access `s' are
ccid3_hc_tx_no_feedback_timer - safe, since first started at the time where `s' is seeded
ccid3_hc_tx_packet_recv - safe, since this is after `s' has been seeded
ccid3_calc_new_t_ipi - safe, since first called after sending or upon feedback
ccid3_hc_tx_update_x - safe, since first called upon feedback or within
ccid3_hc_tx_no_feedback_timer
--all apart from no_feedback_timer are safe since the first time that these are called is
when the first feedback arrives (i.e. after `s' bytes have been sent and s is not 0)
--ccid3_hc_tx_no_feedback_timer has an issue if
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 59 +++++++++++++++++++++++++++++++++----------------
1 file changed, 40 insertions(+), 19 deletions(-)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -151,6 +151,24 @@ static void ccid3_hc_tx_update_x(struct
}
}
+/*
+ * Track the mean packet size `s' (cf. RFC 4342, 5.3 and RFC 3448, 4.1)
+ * @len: DCCP packet payload size in bytes
+ */
+static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len)
+{
+ if(len == 0)
+ ccid3_pr_debug("Packet payload length is 0 - not updating\n");
+ else
+ hctx->ccid3hctx_s = (hctx->ccid3hctx_s == 0)? len
+ : (9 * hctx->ccid3hctx_s + len) / 10;
+
+ /* Note: We could do a potential optimisation here - when `s' changes,
+ recalculate sending rate and consequently t_ipi, t_delta, and
+ t_now. This is however non-standard, and the benefits are not
+ clear, so it is currently left out. */
+}
+
static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
{
struct sock *sk = (struct sock *)data;
@@ -297,6 +315,10 @@ static int ccid3_hc_tx_send_packet(struc
hctx->ccid3hctx_t_last_win_count = now;
ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
+ /* Set initial sending rate to 1 packet per second */
+ ccid3_hc_tx_update_s(hctx, len);
+ hctx->ccid3hctx_x = hctx->ccid3hctx_s;
+
/* First timeout, according to [RFC 3448, 4.2], is 1 second */
hctx->ccid3hctx_t_ipi = USEC_PER_SEC;
/* Initial delta: minimum of 0.5 sec and t_gran/2 */
@@ -348,6 +370,8 @@ static void ccid3_hc_tx_packet_sent(stru
unsigned long quarter_rtt;
struct dccp_tx_hist_entry *packet;
+ ccid3_hc_tx_update_s(hctx, len);
+
packet = dccp_tx_hist_head(&hctx->ccid3hctx_hist);
if (unlikely(packet == NULL)) {
DCCP_WARN("packet doesn't exist in history!\n");
@@ -626,17 +650,9 @@ static int ccid3_hc_tx_parse_options(str
static int ccid3_hc_tx_init(struct ccid *ccid, struct sock *sk)
{
- struct dccp_sock *dp = dccp_sk(sk);
struct ccid3_hc_tx_sock *hctx = ccid_priv(ccid);
- if (dp->dccps_packet_size >= TFRC_MIN_PACKET_SIZE &&
- dp->dccps_packet_size <= TFRC_MAX_PACKET_SIZE)
- hctx->ccid3hctx_s = dp->dccps_packet_size;
- else
- hctx->ccid3hctx_s = TFRC_STD_PACKET_SIZE;
-
- /* Set transmission rate to 1 packet per second */
- hctx->ccid3hctx_x = hctx->ccid3hctx_s;
+ hctx->ccid3hctx_s = 0;
hctx->ccid3hctx_t_rto = USEC_PER_SEC;
hctx->ccid3hctx_state = TFRC_SSTATE_NO_SENT;
INIT_LIST_HEAD(&hctx->ccid3hctx_hist);
@@ -691,6 +707,15 @@ static void ccid3_hc_rx_set_state(struct
hcrx->ccid3hcrx_state = state;
}
+static inline void ccid3_hc_rx_update_s(struct ccid3_hc_rx_sock *hcrx, int len)
+{
+ if(len == 0) /* don't update on empty packets (e.g. ACKs) */
+ ccid3_pr_debug("Packet payload length is 0 - not updating\n");
+ else
+ hcrx->ccid3hcrx_s = (hcrx->ccid3hcrx_s == 0)? len
+ : (9 * hcrx->ccid3hcrx_s + len) / 10;
+}
+
static void ccid3_hc_rx_send_feedback(struct sock *sk)
{
struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
@@ -967,7 +992,7 @@ static void ccid3_hc_rx_packet_recv(stru
struct dccp_rx_hist_entry *packet;
struct timeval now;
u32 p_prev, rtt_prev, r_sample, t_elapsed;
- int loss;
+ int loss, payload_size;
BUG_ON(hcrx == NULL);
@@ -1022,6 +1047,9 @@ static void ccid3_hc_rx_packet_recv(stru
if (DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK)
return;
+ payload_size = skb->len - dccp_hdr(skb)->dccph_doff * 4;
+ ccid3_hc_rx_update_s(hcrx, payload_size);
+
switch (hcrx->ccid3hcrx_state) {
case TFRC_RSTATE_NO_DATA:
ccid3_pr_debug("%s, sk=%p(%s), skb=%p, sending initial "
@@ -1032,8 +1060,7 @@ static void ccid3_hc_rx_packet_recv(stru
ccid3_hc_rx_set_state(sk, TFRC_RSTATE_DATA);
return;
case TFRC_RSTATE_DATA:
- hcrx->ccid3hcrx_bytes_recv += skb->len -
- dccp_hdr(skb)->dccph_doff * 4;
+ hcrx->ccid3hcrx_bytes_recv += payload_size;
if (loss)
break;
@@ -1073,22 +1100,16 @@ static void ccid3_hc_rx_packet_recv(stru
static int ccid3_hc_rx_init(struct ccid *ccid, struct sock *sk)
{
- struct dccp_sock *dp = dccp_sk(sk);
struct ccid3_hc_rx_sock *hcrx = ccid_priv(ccid);
ccid3_pr_debug("%s, sk=%p\n", dccp_role(sk), sk);
- if (dp->dccps_packet_size >= TFRC_MIN_PACKET_SIZE &&
- dp->dccps_packet_size <= TFRC_MAX_PACKET_SIZE)
- hcrx->ccid3hcrx_s = dp->dccps_packet_size;
- else
- hcrx->ccid3hcrx_s = TFRC_STD_PACKET_SIZE;
-
hcrx->ccid3hcrx_state = TFRC_RSTATE_NO_DATA;
INIT_LIST_HEAD(&hcrx->ccid3hcrx_hist);
INIT_LIST_HEAD(&hcrx->ccid3hcrx_li_hist);
dccp_timestamp(sk, &hcrx->ccid3hcrx_tstamp_last_ack);
hcrx->ccid3hcrx_tstamp_last_feedback = hcrx->ccid3hcrx_tstamp_last_ack;
+ hcrx->ccid3hcrx_s = 0;
hcrx->ccid3hcrx_rtt = 5000; /* XXX 5ms for now... */
return 0;
}
-
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