[CCID3]: Ignore trivial amounts of elapsed time

This patch fixes a previously undiscovered bug; the problem 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 reduces the socket structure by another four bytes.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 1 insertions, 11 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 5bf110b28abc..c025236ce49b 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -744,11 +744,6 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk)
         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 = ktime_us_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) {
@@ -778,10 +773,7 @@ static int ccid3_hc_rx_insert_options(struct sock *sk, struct sk_buff *skb)
         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,
diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h
index 0cdc982cfe47..83467c34ed2b 100644
--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -147,7 +147,6 @@ 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;
@@ -165,7 +164,6 @@ 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_rx_sock *ccid3_hc_rx_sk(const struct sock *sk)