[CCID3]: Ignore trivial amounts of elapsed time
This patch fixes a previously undiscovered bug:
* the receive timestamp is taken when the skb enters the CCID3 module;
* RFC 4342 requires to send an Elapsed Time estimate to the sender;
* the bug is in computing the elapsed time as the time between `receiving'
the packet (i.e. skb enters CCID module) and sending feedback,
--> there is no layer-processing, queueing, or delay involved,
--> hence the elapsed time is in the order of 1 function call
--> this is in the dimension of maximally 50..100usec
--> which renders the use of elapsed time almost entirely useless.
The fix is simply to ignore such trivial amounts of elapsed time.
As a further advantage, the now useless elapsed_time field can be removed from
the socket, which slims the socket structure down by another full four bytes.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 10 +---------
net/dccp/ccids/ccid3.h | 2 --
2 files changed, 1 insertion(+), 11 deletions(-)
--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -140,7 +140,6 @@ enum ccid3_hc_rx_states {
* @ccid3hcrx_li_hist - Loss Interval History
* @ccid3hcrx_s - Received packet size in bytes
* @ccid3hcrx_pinv - Inverse of Loss Event Rate (RFC 4342, sec. 8.5)
- * @ccid3hcrx_elapsed_time - Time since packet reception
*/
struct ccid3_hc_rx_sock {
struct tfrc_rx_info ccid3hcrx_tfrc;
@@ -158,7 +157,6 @@ struct ccid3_hc_rx_sock {
struct list_head ccid3hcrx_li_hist;
u16 ccid3hcrx_s;
u32 ccid3hcrx_pinv;
- u32 ccid3hcrx_elapsed_time;
};
static inline struct ccid3_hc_tx_sock *ccid3_hc_tx_sk(const struct sock *sk)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -764,11 +764,6 @@ static void ccid3_hc_rx_send_feedback(st
hcrx->ccid3hcrx_ccval_last_counter = packet->dccphrx_ccval;
hcrx->ccid3hcrx_bytes_recv = 0;
- /* Elapsed time information [RFC 4340, 13.2] in units of 10 * usecs */
- delta = timeval_delta(&now, &packet->dccphrx_tstamp);
- DCCP_BUG_ON(delta < 0);
- hcrx->ccid3hcrx_elapsed_time = delta / 10;
-
if (hcrx->ccid3hcrx_p == 0)
hcrx->ccid3hcrx_pinv = ~0U; /* see RFC 4342, 8.5 */
else if (hcrx->ccid3hcrx_p > 1000000) {
@@ -799,10 +794,7 @@ static int ccid3_hc_rx_insert_options(st
x_recv = htonl(hcrx->ccid3hcrx_x_recv);
pinv = htonl(hcrx->ccid3hcrx_pinv);
- if ((hcrx->ccid3hcrx_elapsed_time != 0 &&
- dccp_insert_option_elapsed_time(sk, skb,
- hcrx->ccid3hcrx_elapsed_time)) ||
- dccp_insert_option_timestamp(sk, skb) ||
+ if (dccp_insert_option_timestamp(sk, skb) ||
dccp_insert_option(sk, skb, TFRC_OPT_LOSS_EVENT_RATE,
&pinv, sizeof(pinv)) ||
dccp_insert_option(sk, skb, TFRC_OPT_RECEIVE_RATE,
-
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