#include "tcp_vegas.h"
-/* Default values of the Vegas variables, in fixed-point representation
- * with V_PARAM_SHIFT bits to the right of the binary point.
- */
-#define V_PARAM_SHIFT 1
-static int alpha = 2<<V_PARAM_SHIFT;
-static int beta = 4<<V_PARAM_SHIFT;
-static int gamma = 1<<V_PARAM_SHIFT;
+static int alpha = 2;
+static int beta = 4;
+static int gamma = 1;
module_param(alpha, int, 0644);
-MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)");
+MODULE_PARM_DESC(alpha, "lower bound of packets in network");
module_param(beta, int, 0644);
-MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)");
+MODULE_PARM_DESC(beta, "upper bound of packets in network");
module_param(gamma, int, 0644);
MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");
return;
}
- /* The key players are v_beg_snd_una and v_beg_snd_nxt.
- *
- * These are so named because they represent the approximate values
- * of snd_una and snd_nxt at the beginning of the current RTT. More
- * precisely, they represent the amount of data sent during the RTT.
- * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
- * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
- * bytes of data have been ACKed during the course of the RTT, giving
- * an "actual" rate of:
- *
- * (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
- *
- * Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
- * because delayed ACKs can cover more than one segment, so they
- * don't line up nicely with the boundaries of RTTs.
- *
- * Another unfortunate fact of life is that delayed ACKs delay the
- * advance of the left edge of our send window, so that the number
- * of bytes we send in an RTT is often less than our cwnd will allow.
- * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
- */
-
if (after(ack, vegas->beg_snd_nxt)) {
/* Do the Vegas once-per-RTT cwnd adjustment. */
- u32 old_wnd, old_snd_cwnd;
-
-
- /* Here old_wnd is essentially the window of data that was
- * sent during the previous RTT, and has all
- * been acknowledged in the course of the RTT that ended
- * with the ACK we just received. Likewise, old_snd_cwnd
- * is the cwnd during the previous RTT.
- */
- old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
- tp->mss_cache;
- old_snd_cwnd = vegas->beg_snd_cwnd;
/* Save the extent of the current window so we can use this
* at the end of the next RTT.
*/
- vegas->beg_snd_una = vegas->beg_snd_nxt;
vegas->beg_snd_nxt = tp->snd_nxt;
- vegas->beg_snd_cwnd = tp->snd_cwnd;
/* We do the Vegas calculations only if we got enough RTT
* samples that we can be reasonably sure that we got
*
* This is:
* (actual rate in segments) * baseRTT
- * We keep it as a fixed point number with
- * V_PARAM_SHIFT bits to the right of the binary point.
*/
- target_cwnd = ((u64)old_wnd * vegas->baseRTT);
- target_cwnd <<= V_PARAM_SHIFT;
- do_div(target_cwnd, rtt);
+ target_cwnd = tp->snd_cwnd * vegas->baseRTT / rtt;
/* Calculate the difference between the window we had,
* and the window we would like to have. This quantity
* is the "Diff" from the Arizona Vegas papers.
- *
- * Again, this is a fixed point number with
- * V_PARAM_SHIFT bits to the right of the binary
- * point.
*/
- diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
+ diff = tp->snd_cwnd * (rtt-vegas->baseRTT) / vegas->baseRTT;
if (diff > gamma && tp->snd_ssthresh > 2 ) {
/* Going too fast. Time to slow down
* truncation robs us of full link
* utilization.
*/
- tp->snd_cwnd = min(tp->snd_cwnd,
- ((u32)target_cwnd >>
- V_PARAM_SHIFT)+1);
+ tp->snd_cwnd = min(tp->snd_cwnd, (u32)target_cwnd+1);
} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
/* Slow start. */
tcp_slow_start(tp);
} else {
/* Congestion avoidance. */
- u32 next_snd_cwnd;
/* Figure out where we would like cwnd
* to be.
/* The old window was too fast, so
* we slow down.
*/
- next_snd_cwnd = old_snd_cwnd - 1;
+ tp->snd_cwnd--;
} else if (diff < alpha) {
/* We don't have enough extra packets
* in the network, so speed up.
*/
- next_snd_cwnd = old_snd_cwnd + 1;
+ tp->snd_cwnd++;
} else {
/* Sending just as fast as we
* should be.
*/
- next_snd_cwnd = old_snd_cwnd;
}
-
- /* Adjust cwnd upward or downward, toward the
- * desired value.
- */
- if (next_snd_cwnd > tp->snd_cwnd)
- tp->snd_cwnd++;
- else if (next_snd_cwnd < tp->snd_cwnd)
- tp->snd_cwnd--;
}
if (tp->snd_cwnd < 2)
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff