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Diffstat (limited to 'net/ipv4/tcp_cubic.c')
-rw-r--r--net/ipv4/tcp_cubic.c81
1 files changed, 41 insertions, 40 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 9a582fb4ef9f..14224487b16b 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -1,5 +1,5 @@
/*
- * TCP CUBIC: Binary Increase Congestion control for TCP v2.0
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.1
*
* This is from the implementation of CUBIC TCP in
* Injong Rhee, Lisong Xu.
@@ -51,8 +51,6 @@ MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_
module_param(tcp_friendliness, int, 0644);
MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
-#include <asm/div64.h>
-
/* BIC TCP Parameters */
struct bictcp {
u32 cnt; /* increase cwnd by 1 after ACKs */
@@ -93,50 +91,51 @@ static void bictcp_init(struct sock *sk)
tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
}
-/* 64bit divisor, dividend and result. dynamic precision */
-static inline u_int64_t div64_64(u_int64_t dividend, u_int64_t divisor)
-{
- u_int32_t d = divisor;
-
- if (divisor > 0xffffffffULL) {
- 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 = (uint32_t) dividend / d;
-
- return dividend;
-}
-
-/*
- * calculate the cubic root of x using Newton-Raphson
+/* calculate the cubic root of x using a table lookup followed by one
+ * Newton-Raphson iteration.
+ * Avg err ~= 0.195%
*/
static u32 cubic_root(u64 a)
{
- u32 x, x1;
-
- /* Initial estimate is based on:
- * cbrt(x) = exp(log(x) / 3)
+ u32 x, b, shift;
+ /*
+ * cbrt(x) MSB values for x MSB values in [0..63].
+ * Precomputed then refined by hand - Willy Tarreau
+ *
+ * For x in [0..63],
+ * v = cbrt(x << 18) - 1
+ * cbrt(x) = (v[x] + 10) >> 6
*/
- x = 1u << (fls64(a)/3);
+ static const u8 v[] = {
+ /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
+ /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
+ /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
+ /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
+ /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
+ /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
+ /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
+ /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
+ };
+
+ b = fls64(a);
+ if (b < 7) {
+ /* a in [0..63] */
+ return ((u32)v[(u32)a] + 35) >> 6;
+ }
+
+ b = ((b * 84) >> 8) - 1;
+ shift = (a >> (b * 3));
+
+ x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
/*
- * Iteration based on:
+ * Newton-Raphson iteration
* 2
* x = ( 2 * x + a / x ) / 3
* k+1 k k
*/
- do {
- x1 = x;
- x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3;
- } while (abs(x1 - x) > 1);
-
+ x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));
+ x = ((x * 341) >> 10);
return x;
}
@@ -215,7 +214,9 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
if (ca->delay_min > 0) {
/* max increment = Smax * rtt / 0.1 */
min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
- if (ca->cnt < min_cnt)
+
+ /* use concave growth when the target is above the origin */
+ if (ca->cnt < min_cnt && t >= ca->bic_K)
ca->cnt = min_cnt;
}
@@ -333,7 +334,7 @@ static void bictcp_state(struct sock *sk, u8 new_state)
/* Track delayed acknowledgment ratio using sliding window
* ratio = (15*ratio + sample) / 16
*/
-static void bictcp_acked(struct sock *sk, u32 cnt)
+static void bictcp_acked(struct sock *sk, u32 cnt, ktime_t last)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -401,4 +402,4 @@ module_exit(cubictcp_unregister);
MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CUBIC TCP");
-MODULE_VERSION("2.0");
+MODULE_VERSION("2.1");