[PATCH] TCP Compound: dwnd=0 on ssthresh
In the TCP Compound article used as a reference for the implementation, we read:
"If a retransmission timeout occurs, dwnd should be reset to zero and
the delay-based component is disabled." at page 5 of
ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf
The attached patch implements this requirement.
Regards,
Angelo P. Castellani
diff -urd a/net/ipv4/tcp_compound.c b/net/ipv4/tcp_compound.c
--- a/net/ipv4/tcp_compound.c 2006-07-05 17:19:28.0 +0200
+++ b/net/ipv4/tcp_compound.c 2006-07-05 17:20:42.0 +0200
@@ -221,12 +221,9 @@
tcp_compound_init(sk);
}
-static void tcp_compound_cong_avoid(struct sock *sk, u32 ack,
-u32 seq_rtt, u32 in_flight, int flag)
-{
+static inline void tcp_compound_synch(struct sock *sk) {
struct tcp_sock *tp = tcp_sk(sk);
struct compound *vegas = inet_csk_ca(sk);
- u8 inc = 0;
if (vegas->cwnd + vegas->dwnd > tp->snd_cwnd) {
if (vegas->cwnd > tp->snd_cwnd || vegas->dwnd > tp->snd_cwnd) {
@@ -234,9 +231,19 @@
vegas->dwnd = 0;
} else
vegas->cwnd = tp->snd_cwnd - vegas->dwnd;
-
}
+}
+
+static void tcp_compound_cong_avoid(struct sock *sk, u32 ack,
+u32 seq_rtt, u32 in_flight, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct compound *vegas = inet_csk_ca(sk);
+ u8 inc = 0;
+
+ tcp_compound_synch(sk);
+
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
@@ -415,9 +422,21 @@
}
}
+static u32 tcp_compound_ssthresh(struct sock *sk) {
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct compound *vegas = inet_csk_ca(sk);
+
+ tcp_compound_synch(sk);
+
+ vegas->dwnd = 0;
+ tp->snd_cwnd = vegas->cwnd;
+
+ return tcp_reno_ssthresh(sk);
+}
+
static struct tcp_congestion_ops tcp_compound = {
.init = tcp_compound_init,
- .ssthresh = tcp_reno_ssthresh,
+ .ssthresh = tcp_compound_ssthresh,
.cong_avoid = tcp_compound_cong_avoid,
.min_cwnd = tcp_reno_min_cwnd,
.rtt_sample = tcp_compound_rtt_calc,
Re: [PATCH] TCP Compound
The existing code did a 64 bit divide directly, which won't work on
32 bit platforms. This is what I am testing, it uses math similar to
TCP CUBIC to do a quad root. It seemed more efficient to just do
one operation rather than two square roots.
-
diff --git a/net/ipv4/tcp_compound.c b/net/ipv4/tcp_compound.c
index 01048e2..74c26a0 100644
--- a/net/ipv4/tcp_compound.c
+++ b/net/ipv4/tcp_compound.c
@@ -52,8 +52,6 @@
#define TCP_COMPOUND_ALPHA 3U
#define TCP_COMPOUND_BETA 1U
-#define TCP_COMPOUND_KAPPA_POW 3
-#define TCP_COMPOUND_KAPPA_NSQRT2
#define TCP_COMPOUND_GAMMA 30
#define TCP_COMPOUND_ZETA 1
@@ -156,6 +154,58 @@ static void tcp_compound_state(struct so
vegas_disable(sk);
}
+
+/* 64bit divisor, dividend and result. dynamic precision */
+static inline u64 div64_64(u64 dividend, u64 divisor)
+{
+ u32 d = divisor;
+
+ if (divisor > 0xULL) {
+ unsigned int shift = fls(divisor >> 32);
+
+ d = divisor >> shift;
+ dividend >>= shift;
+ }
+
+ /* avoid 64 bit division if possible */
+ if (dividend >> 32)
+ do_div(dividend, d);
+ else
+ dividend = (u32) dividend / d;
+
+ return dividend;
+}
+
+/* calculate the quartic root of "a" using Newton-Raphson */
+static u32 qroot(u64 a)
+{
+ u32 x, x1;
+
+ /* Initial estimate is based on:
+* qrt(x) = exp(log(x) / 4)
+*/
+ x = 1u << (fls64(a) >> 2);
+
+ /*
+* Iteration based on:
+* 3
+* x= ( 3 * x + a / x ) / 4
+* k+1 k k
+*/
+ do {
+ u64 x3 = x;
+
+ x1 = x;
+ x3 *= x;
+ x3 *= x;
+
+ x = (3 * x + (u32) div64_64(a, x3)) / 4;
+ } while (abs(x1 - x) > 1);
+
+ return x;
+}
+
+
/*
* If the connection is idle and we are restarting,
* then we don't want to do any Vegas calculations
@@ -307,29 +357,23 @@ static void tcp_compound_cong_avoid(stru
dwnd = vegas->dwnd;
if (diff < (TCP_COMPOUND_GAMMA << V_PARAM_SHIFT)) {
- u32 i, j, x, x2;
- u64 v;
-
- v = 1;
-
- for (i = 0; i < TCP_COMPOUND_KAPPA_POW; i++)
- v *= old_wnd;
-
- for (i = 0; i < TCP_COMPOUND_KAPPA_NSQRT; i++) {
- x = 1;
- for (j = 0; j < 200; j++) {
- x2 = (x + v / x) / 2;
-
- if (x2 == x || !x2)
- break;
-
- x = x2;
- }
- v = x;
- }
+ u64 win3;
- x = (u32) v >> TCP_COMPOUND_ALPHA;
+ /*
+* The TCP Compound paper describes the choice
+* of "k" determines the agressiveness,
+* ie. slope of the response function.
+*
+* For same value as HSTCP would be 0.8
+* but for computaional reasons, both the
+* original authors and this implementation
+* use 0.75.
+*/
+ win3 = old_wnd;
+ win3 *= old_wnd;
+ win3 *= old_wnd;
+ x = qroot(win3) >> TCP_COMPOUND_ALPHA;
if (x > 1)
dwnd = x - 1;
else
-
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[PATCH] TCP Compound
From: Angelo P. Castellani <[EMAIL PROTECTED]>
TCP Compound is a sender-side only change to TCP that uses
a mixed Reno/Vegas approach to calculate the cwnd.
For further details look here:
ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf
Signed-off-by: Angelo P. Castellani <[EMAIL PROTECTED]>
---
This new revision of the TCP Compound implementation fixes some issues
present in the previous patch and has been reverted to a stand-alone
file (thanks to Stephen suggestion).
Regards,
Angelo P. Castellani
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 326676b..e577eb8 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -542,6 +542,16 @@ config TCP_CONG_LP
``fair share`` of bandwidth as targeted by TCP.
See http://www-ece.rice.edu/networks/TCP-LP/
+config TCP_CONG_COMPOUND
+ tristate "TCP Compound"
+ depends on EXPERIMENTAL
+ default n
+ ---help---
+ TCP Compound is a sender-side only change to TCP that uses
+ a mixed Reno/Vegas approach to calculate the cwnd.
+ For further details look here:
+ ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf
+
endmenu
config TCP_CONG_BIC
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index 5c65487..f0697c4 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -43,6 +43,7 @@ obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.
obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o
+obj-$(CONFIG_TCP_CONG_COMPOUND) += tcp_compound.o
obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
xfrm4_output.o
/*
* TCP Vegas congestion control
*
* This is based on the congestion detection/avoidance scheme described in
*Lawrence S. Brakmo and Larry L. Peterson.
*"TCP Vegas: End to end congestion avoidance on a global internet."
*IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
*October 1995. Available from:
* ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
*
* See http://www.cs.arizona.edu/xkernel/ for their implementation.
* The main aspects that distinguish this implementation from the
* Arizona Vegas implementation are:
* o We do not change the loss detection or recovery mechanisms of
* Linux in any way. Linux already recovers from losses quite well,
* using fine-grained timers, NewReno, and FACK.
* o To avoid the performance penalty imposed by increasing cwnd
* only every-other RTT during slow start, we increase during
* every RTT during slow start, just like Reno.
* o Largely to allow continuous cwnd growth during slow start,
* we use the rate at which ACKs come back as the "actual"
* rate, rather than the rate at which data is sent.
* o To speed convergence to the right rate, we set the cwnd
* to achieve the right ("actual") rate when we exit slow start.
* o To filter out the noise caused by delayed ACKs, we use the
* minimum RTT sample observed during the last RTT to calculate
* the actual rate.
* o When the sender re-starts from idle, it waits until it has
* received ACKs for an entire flight of new data before making
* a cwnd adjustment decision. The original Vegas implementation
* assumed senders never went idle.
*
*
* TCP Compound based on TCP Vegas
*
* further details can be found here:
* ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf
*/
#include
#include
#include
#include
#include
#include
/* 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
#define TCP_COMPOUND_ALPHA 3U
#define TCP_COMPOUND_BETA 1U
#define TCP_COMPOUND_KAPPA_POW 3
#define TCP_COMPOUND_KAPPA_NSQRT2
#define TCP_COMPOUND_GAMMA 30
#define TCP_COMPOUND_ZETA 1
/* TCP compound variables */
struct compound {
u32 beg_snd_nxt; /* right edge during last RTT */
u32 beg_snd_una; /* left edge during last RTT */
u32 beg_snd_cwnd; /* saves the size of the cwnd */
u8 doing_vegas_now; /* if true, do vegas for this RTT */
u16 cntRTT; /* # of RTTs measured within last RTT */
u32 minRTT; /* min of RTTs measured within last RTT (in usec) */
u32 baseRTT; /* the min of all Vegas RTT measurements seen (in usec) */
u32 cwnd;
u32 dwnd;
};
/* There are several situations when we must "re-start" Vegas:
*
* o when a connection is established
* o after an RTO
* o after fast recovery
* o when we send a packet and there is no outstanding
*unacknowledged data (restarting an idle connection)
*
* In these circumstances we cannot do a Vegas calculation at the
* end of the first RTT, because any calculation we do is using
* stale info -- both the saved cwnd and congestion feedback are
* stale.
*
* Instead we must wait until the completion of an RTT during
* which we actually receive ACKs.
*/
static inline void vegas_enable(struct sock *sk)
{
const str
