[TCP] BIC: CUBIC window growth (2.0)
Replace existing BIC version 1.1 with new version 2.0. The main change is to replace the window growth function with a cubic function as described in: http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf Signed-off-by: Stephen Hemminger <shemminger@osdl.org> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Stephen Hemminger
David S. Miller
Родитель
05d054503a
Коммит
df3271f336
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@ -456,6 +456,14 @@ config TCP_CONG_BIC
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increase provides TCP friendliness.
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See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/
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config TCP_CONG_CUBIC
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tristate "CUBIC TCP"
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default m
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---help---
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This is version 2.0 of BIC-TCP which uses a cubic growth function
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among other techniques.
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See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
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config TCP_CONG_WESTWOOD
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tristate "TCP Westwood+"
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default m
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@ -34,6 +34,7 @@ obj-$(CONFIG_INET_DIAG) += inet_diag.o
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obj-$(CONFIG_IP_ROUTE_MULTIPATH_CACHED) += multipath.o
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obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
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obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
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obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o
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obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o
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obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
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obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
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@ -0,0 +1,445 @@
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/*
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* TCP CUBIC: Binary Increase Congestion control for TCP v2.0
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*
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* This is from the implementation of CUBIC TCP in
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* Injong Rhee, Lisong Xu.
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* "CUBIC: A New TCP-Friendly High-Speed TCP Variant
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* in PFLDnet 2005
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* Available from:
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* http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
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*
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* Unless CUBIC is enabled and congestion window is large
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* this behaves the same as the original Reno.
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*/
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#include <linux/config.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <net/tcp.h>
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#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
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* max_cwnd = snd_cwnd * beta
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*/
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#define BICTCP_B 4 /*
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* In binary search,
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* go to point (max+min)/N
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*/
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#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
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static int fast_convergence = 1;
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static int max_increment = 16;
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static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
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static int initial_ssthresh = 100;
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static int bic_scale = 41;
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static int tcp_friendliness = 1;
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module_param(fast_convergence, int, 0644);
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MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
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module_param(max_increment, int, 0644);
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MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
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module_param(beta, int, 0644);
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MODULE_PARM_DESC(beta, "beta for multiplicative increase");
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module_param(initial_ssthresh, int, 0644);
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MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
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module_param(bic_scale, int, 0644);
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MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
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module_param(tcp_friendliness, int, 0644);
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MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
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/* BIC TCP Parameters */
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struct bictcp {
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u32 cnt; /* increase cwnd by 1 after ACKs */
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u32 last_max_cwnd; /* last maximum snd_cwnd */
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u32 loss_cwnd; /* congestion window at last loss */
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u32 last_cwnd; /* the last snd_cwnd */
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u32 last_time; /* time when updated last_cwnd */
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u32 bic_origin_point;/* origin point of bic function */
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u32 bic_K; /* time to origin point from the beginning of the current epoch */
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u32 delay_min; /* min delay */
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u32 epoch_start; /* beginning of an epoch */
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u32 ack_cnt; /* number of acks */
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u32 tcp_cwnd; /* estimated tcp cwnd */
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#define ACK_RATIO_SHIFT 4
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u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
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};
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static inline void bictcp_reset(struct bictcp *ca)
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{
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ca->cnt = 0;
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ca->last_max_cwnd = 0;
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ca->loss_cwnd = 0;
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ca->last_cwnd = 0;
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ca->last_time = 0;
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ca->bic_origin_point = 0;
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ca->bic_K = 0;
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ca->delay_min = 0;
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ca->epoch_start = 0;
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ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
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ca->ack_cnt = 0;
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ca->tcp_cwnd = 0;
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}
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static void bictcp_init(struct sock *sk)
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{
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bictcp_reset(inet_csk_ca(sk));
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if (initial_ssthresh)
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tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
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}
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/* 65536 times the cubic root */
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static const u64 cubic_table[8]
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= {0, 65536, 82570, 94519, 104030, 112063, 119087, 125367};
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/*
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* calculate the cubic root of x
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* the basic idea is that x can be expressed as i*8^j
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* so cubic_root(x) = cubic_root(i)*2^j
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* in the following code, x is i, and y is 2^j
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* because of integer calculation, there are errors in calculation
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* so finally use binary search to find out the exact solution
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*/
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static u32 cubic_root(u64 x)
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{
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u64 y, app, target, start, end, mid, start_diff, end_diff;
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if (x == 0)
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return 0;
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target = x;
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/* first estimate lower and upper bound */
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y = 1;
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while (x >= 8){
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x = (x >> 3);
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y = (y << 1);
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}
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start = (y*cubic_table[x])>>16;
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if (x==7)
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end = (y<<1);
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else
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end = (y*cubic_table[x+1]+65535)>>16;
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/* binary search for more accurate one */
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while (start < end-1) {
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mid = (start+end) >> 1;
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app = mid*mid*mid;
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if (app < target)
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start = mid;
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else if (app > target)
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end = mid;
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else
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return mid;
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}
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/* find the most accurate one from start and end */
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app = start*start*start;
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if (app < target)
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start_diff = target - app;
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else
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start_diff = app - target;
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app = end*end*end;
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if (app < target)
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end_diff = target - app;
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else
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end_diff = app - target;
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if (start_diff < end_diff)
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return (u32)start;
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else
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return (u32)end;
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}
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static inline u32 bictcp_K(u32 dist, u32 srtt)
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{
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u64 d64;
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u32 d32;
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u32 count;
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u32 result;
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/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
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so K = cubic_root( (wmax-cwnd)*rtt/c )
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the unit of K is bictcp_HZ=2^10, not HZ
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c = bic_scale >> 10
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rtt = (tp->srtt >> 3 ) / HZ
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the following code has been designed and tested for
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cwnd < 1 million packets
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RTT < 100 seconds
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HZ < 1,000,00 (corresponding to 10 nano-second)
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*/
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/* 1/c * 2^2*bictcp_HZ */
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d32 = (1 << (10+2*BICTCP_HZ)) / bic_scale;
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d64 = (__u64)d32;
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/* srtt * 2^count / HZ
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1) to get a better accuracy of the following d32,
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the larger the "count", the better the accuracy
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2) and avoid overflow of the following d64
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the larger the "count", the high possibility of overflow
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3) so find a "count" between bictcp_hz-3 and bictcp_hz
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"count" may be less than bictcp_HZ,
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then d64 becomes 0. that is OK
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*/
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d32 = srtt;
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count = 0;
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while (((d32 & 0x80000000)==0) && (count < BICTCP_HZ)){
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d32 = d32 << 1;
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count++;
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}
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d32 = d32 / HZ;
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/* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) */
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d64 = (d64 * dist * d32) >> (count+3-BICTCP_HZ);
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/* cubic root */
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d64 = cubic_root(d64);
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result = (u32)d64;
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return result;
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}
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/*
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* Compute congestion window to use.
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*/
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static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
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{
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u64 d64;
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u32 d32, t, srtt, bic_target, min_cnt, max_cnt;
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ca->ack_cnt++; /* count the number of ACKs */
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if (ca->last_cwnd == cwnd &&
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(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
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return;
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ca->last_cwnd = cwnd;
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ca->last_time = tcp_time_stamp;
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srtt = (HZ << 3)/10; /* use real time-based growth function */
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if (ca->epoch_start == 0) {
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ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
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ca->ack_cnt = 1; /* start counting */
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ca->tcp_cwnd = cwnd; /* syn with cubic */
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if (ca->last_max_cwnd <= cwnd) {
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ca->bic_K = 0;
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ca->bic_origin_point = cwnd;
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} else {
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ca->bic_K = bictcp_K(ca->last_max_cwnd-cwnd, srtt);
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ca->bic_origin_point = ca->last_max_cwnd;
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}
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}
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/* cubic function - calc*/
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/* calculate c * time^3 / rtt,
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* while considering overflow in calculation of time^3
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* (so time^3 is done by using d64)
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* and without the support of division of 64bit numbers
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* (so all divisions are done by using d32)
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* also NOTE the unit of those veriables
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* time = (t - K) / 2^bictcp_HZ
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* c = bic_scale >> 10
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* rtt = (srtt >> 3) / HZ
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* !!! The following code does not have overflow problems,
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* if the cwnd < 1 million packets !!!
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*/
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/* change the unit from HZ to bictcp_HZ */
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t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start)
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<< BICTCP_HZ) / HZ;
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if (t < ca->bic_K) /* t - K */
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d32 = ca->bic_K - t;
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else
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d32 = t - ca->bic_K;
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d64 = (u64)d32;
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d32 = (bic_scale << 3) * HZ / srtt; /* 1024*c/rtt */
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d64 = (d32 * d64 * d64 * d64) >> (10+3*BICTCP_HZ); /* c/rtt * (t-K)^3 */
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d32 = (u32)d64;
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if (t < ca->bic_K) /* below origin*/
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bic_target = ca->bic_origin_point - d32;
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else /* above origin*/
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bic_target = ca->bic_origin_point + d32;
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/* cubic function - calc bictcp_cnt*/
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if (bic_target > cwnd) {
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ca->cnt = cwnd / (bic_target - cwnd);
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} else {
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ca->cnt = 100 * cwnd; /* very small increment*/
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}
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if (ca->delay_min > 0) {
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/* max increment = Smax * rtt / 0.1 */
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min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
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if (ca->cnt < min_cnt)
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ca->cnt = min_cnt;
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}
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/* slow start and low utilization */
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if (ca->loss_cwnd == 0) /* could be aggressive in slow start */
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ca->cnt = 50;
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/* TCP Friendly */
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if (tcp_friendliness) {
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u32 scale = 8*(BICTCP_BETA_SCALE+beta)/3/(BICTCP_BETA_SCALE-beta);
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d32 = (cwnd * scale) >> 3;
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while (ca->ack_cnt > d32) { /* update tcp cwnd */
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ca->ack_cnt -= d32;
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ca->tcp_cwnd++;
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}
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if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
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d32 = ca->tcp_cwnd - cwnd;
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max_cnt = cwnd / d32;
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if (ca->cnt > max_cnt)
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ca->cnt = max_cnt;
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}
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}
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ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
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if (ca->cnt == 0) /* cannot be zero */
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ca->cnt = 1;
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}
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/* Keep track of minimum rtt */
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static inline void measure_delay(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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struct bictcp *ca = inet_csk_ca(sk);
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u32 delay;
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/* No time stamp */
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if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
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/* Discard delay samples right after fast recovery */
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(s32)(tcp_time_stamp - ca->epoch_start) < HZ)
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return;
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delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
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if (delay == 0)
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delay = 1;
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/* first time call or link delay decreases */
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if (ca->delay_min == 0 || ca->delay_min > delay)
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ca->delay_min = delay;
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}
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static void bictcp_cong_avoid(struct sock *sk, u32 ack,
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u32 seq_rtt, u32 in_flight, int data_acked)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct bictcp *ca = inet_csk_ca(sk);
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if (data_acked)
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measure_delay(sk);
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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else {
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bictcp_update(ca, tp->snd_cwnd);
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/* In dangerous area, increase slowly.
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* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
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*/
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if (tp->snd_cwnd_cnt >= ca->cnt) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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} else
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tp->snd_cwnd_cnt++;
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}
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}
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static u32 bictcp_recalc_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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struct bictcp *ca = inet_csk_ca(sk);
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ca->epoch_start = 0; /* end of epoch */
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/* Wmax and fast convergence */
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if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
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ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
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/ (2 * BICTCP_BETA_SCALE);
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else
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ca->last_max_cwnd = tp->snd_cwnd;
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ca->loss_cwnd = tp->snd_cwnd;
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return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
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}
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static u32 bictcp_undo_cwnd(struct sock *sk)
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{
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struct bictcp *ca = inet_csk_ca(sk);
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return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
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}
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static u32 bictcp_min_cwnd(struct sock *sk)
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{
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return tcp_sk(sk)->snd_ssthresh;
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}
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static void bictcp_state(struct sock *sk, u8 new_state)
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{
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if (new_state == TCP_CA_Loss)
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bictcp_reset(inet_csk_ca(sk));
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}
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/* Track delayed acknowledgment ratio using sliding window
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* ratio = (15*ratio + sample) / 16
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*/
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static void bictcp_acked(struct sock *sk, u32 cnt)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
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struct bictcp *ca = inet_csk_ca(sk);
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cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
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ca->delayed_ack += cnt;
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}
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}
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static struct tcp_congestion_ops cubictcp = {
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.init = bictcp_init,
|
||||
.ssthresh = bictcp_recalc_ssthresh,
|
||||
.cong_avoid = bictcp_cong_avoid,
|
||||
.set_state = bictcp_state,
|
||||
.undo_cwnd = bictcp_undo_cwnd,
|
||||
.min_cwnd = bictcp_min_cwnd,
|
||||
.pkts_acked = bictcp_acked,
|
||||
.owner = THIS_MODULE,
|
||||
.name = "cubic",
|
||||
};
|
||||
|
||||
static int __init cubictcp_register(void)
|
||||
{
|
||||
BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
|
||||
return tcp_register_congestion_control(&cubictcp);
|
||||
}
|
||||
|
||||
static void __exit cubictcp_unregister(void)
|
||||
{
|
||||
tcp_unregister_congestion_control(&cubictcp);
|
||||
}
|
||||
|
||||
module_init(cubictcp_register);
|
||||
module_exit(cubictcp_unregister);
|
||||
|
||||
MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
|
||||
MODULE_LICENSE("GPL");
|
||||
MODULE_DESCRIPTION("CUBIC TCP");
|
||||
MODULE_VERSION("2.0");
|
||||
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