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tcp: cubic improvements

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- avoid cwnd excessive increments on threshold changes
- fix K computation when fastconvergence is on

Change-Id: I99c36abc879e63aecc0617f7aed5a2f68430ba71
Signed-off-by: Florin Coras <fcoras@cisco.com>
This commit is contained in:
Florin Coras
2018-11-13 00:03:43 -08:00
committed by Dave Barach
parent aa01abb2b7
commit 6ebd4398ae
1 changed files with 25 additions and 9 deletions
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34
src/vnet/tcp/tcp_cubic.c
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@@ -69,10 +69,12 @@ W_cubic (cubic_data_t * cd, f64 t)
* RFC 8312 Eq. 2
*/
static inline f64
K_cubic (cubic_data_t * cd)
K_cubic (cubic_data_t * cd, u32 wnd)
{
/* K = cubic_root(W_max*(1-beta_cubic)/C) */
return pow (cd->w_max * (1 - beta_cubic) / cubic_c, 1 / 3.0);
/* K = cubic_root(W_max*(1-beta_cubic)/C)
* Because the current window may be less than W_max * beta_cubic because
* of fast convergence, we pass it as parameter */
return pow ((f64) (cd->w_max - wnd) / cubic_c, 1 / 3.0);
}
/**
@@ -108,8 +110,23 @@ cubic_recovered (tcp_connection_t * tc)
{
cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
cd->t_start = cubic_time (tc->c_thread_index);
cd->K = K_cubic (cd);
tc->cwnd = tc->ssthresh;
cd->K = K_cubic (cd, tc->cwnd / tc->snd_mss);
}
static void
cubic_cwnd_accumulate (tcp_connection_t * tc, u32 thresh, u32 bytes_acked)
{
/* We just updated the threshold and don't know how large the previous
* one was. Still, optimistically increase cwnd by one segment and
* clear the accumulated bytes. */
if (tc->cwnd_acc_bytes > thresh)
{
tc->cwnd += tc->snd_mss;
tc->cwnd_acc_bytes = 0;
}
tcp_cwnd_accumulate (tc, thresh, tc->bytes_acked);
}
static void
@@ -137,7 +154,7 @@ cubic_rcv_ack (tcp_connection_t * tc)
w_aimd = (u64) W_est (cd, t, rtt_sec) * tc->snd_mss;
if (w_cubic < w_aimd)
{
tcp_cwnd_accumulate (tc, tc->cwnd, tc->bytes_acked);
cubic_cwnd_accumulate (tc, tc->cwnd, tc->bytes_acked);
}
else
{
@@ -155,16 +172,15 @@ cubic_rcv_ack (tcp_connection_t * tc)
*/
thresh = (tc->snd_mss * tc->cwnd) / (w_cubic - tc->cwnd);
/* Make sure we don't increase cwnd more often than every
* 2 segments */
thresh = clib_max (thresh, 2 * tc->snd_mss);
/* Make sure we don't increase cwnd more often than every segment */
thresh = clib_max (thresh, tc->snd_mss);
}
else
{
/* Practically we can't increment so just inflate threshold */
thresh = 50 * tc->cwnd;
}
tcp_cwnd_accumulate (tc, thresh, tc->bytes_acked);
cubic_cwnd_accumulate (tc, thresh, tc->bytes_acked);
}
}