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-----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEq5lC5tSkz8NBJiCnSfxwEqXeA64FAmNHYD0ACgkQSfxwEqXe A655AA//dJK0PdRghqrKQsl18GOCffV5TUw5i1VbJQbI9d8anfxNjVUQiNGZi4et qUwZ8OqVXxYx1Z1UDgUE39PjEDSG9/cCvOpMUWqN20/+6955WlNZjwA7Fk6zjvlM R30fz5CIJns9RFvGT4SwKqbVLXIMvfg/wDENUN+8sxt36+VD2gGol7J2JJdngEhM lW+zqzi0ABqYy5so4TU2kixpKmpC08rqFvQbD1GPid+50+JsOiIqftDErt9Eg1Mg MqYivoFCvbAlxxxRh3+UHBd7ZpJLtp1UFEOl2Rf00OXO+ZclLCAQAsTczucIWK9M 8LCZjb7d4lPJv9RpXFAl3R1xvfc+Uy2ga5KeXvufZtc5G3aMUKPuIU7k28ZyblVS XXsXEYhjTSd0tgi3d0JlValrIreSuj0z2QGT5pVcC9utuAqAqRIlosiPmgPlzXjr Us4jXaUhOIPKI+Musv/fqrxsTQziT0jgVA3Njlt4cuAGm/EeUbLUkMWwKXjZLTsv vDsBhEQFmyZqxWu4pYo534VX2mQWTaKRV1SUVVhQEHm57b00EAiZohoOvweB09SR 4KiJapikoopmW4oAUFotUXUL1PM6yi+MXguTuc1SEYuLz/tCFtK8DJVwNpfnWZpE lZKvXyJnHq2Sgod/hEZq58PMvT6aNzTzSg7YzZy+VabxQGOO5mc= =M+mV -----END PGP SIGNATURE----- Merge tag 'random-6.1-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random Pull more random number generator updates from Jason Donenfeld: "This time with some large scale treewide cleanups. The intent of this pull is to clean up the way callers fetch random integers. The current rules for doing this right are: - If you want a secure or an insecure random u64, use get_random_u64() - If you want a secure or an insecure random u32, use get_random_u32() The old function prandom_u32() has been deprecated for a while now and is just a wrapper around get_random_u32(). Same for get_random_int(). - If you want a secure or an insecure random u16, use get_random_u16() - If you want a secure or an insecure random u8, use get_random_u8() - If you want secure or insecure random bytes, use get_random_bytes(). The old function prandom_bytes() has been deprecated for a while now and has long been a wrapper around get_random_bytes() - If you want a non-uniform random u32, u16, or u8 bounded by a certain open interval maximum, use prandom_u32_max() I say "non-uniform", because it doesn't do any rejection sampling or divisions. Hence, it stays within the prandom_*() namespace, not the get_random_*() namespace. I'm currently investigating a "uniform" function for 6.2. We'll see what comes of that. By applying these rules uniformly, we get several benefits: - By using prandom_u32_max() with an upper-bound that the compiler can prove at compile-time is ≤65536 or ≤256, internally get_random_u16() or get_random_u8() is used, which wastes fewer batched random bytes, and hence has higher throughput. - By using prandom_u32_max() instead of %, when the upper-bound is not a constant, division is still avoided, because prandom_u32_max() uses a faster multiplication-based trick instead. - By using get_random_u16() or get_random_u8() in cases where the return value is intended to indeed be a u16 or a u8, we waste fewer batched random bytes, and hence have higher throughput. This series was originally done by hand while I was on an airplane without Internet. Later, Kees and I worked on retroactively figuring out what could be done with Coccinelle and what had to be done manually, and then we split things up based on that. So while this touches a lot of files, the actual amount of code that's hand fiddled is comfortably small" * tag 'random-6.1-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random: prandom: remove unused functions treewide: use get_random_bytes() when possible treewide: use get_random_u32() when possible treewide: use get_random_{u8,u16}() when possible, part 2 treewide: use get_random_{u8,u16}() when possible, part 1 treewide: use prandom_u32_max() when possible, part 2 treewide: use prandom_u32_max() when possible, part 1
428 lines
11 KiB
C
428 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* CAIA Delay-Gradient (CDG) congestion control
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*
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* This implementation is based on the paper:
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* D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using
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* delay gradients." In IFIP Networking, pages 328-341. Springer, 2011.
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*
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* Scavenger traffic (Less-than-Best-Effort) should disable coexistence
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* heuristics using parameters use_shadow=0 and use_ineff=0.
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*
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* Parameters window, backoff_beta, and backoff_factor are crucial for
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* throughput and delay. Future work is needed to determine better defaults,
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* and to provide guidelines for use in different environments/contexts.
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*
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* Except for window, knobs are configured via /sys/module/tcp_cdg/parameters/.
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* Parameter window is only configurable when loading tcp_cdg as a module.
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*
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* Notable differences from paper/FreeBSD:
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* o Using Hybrid Slow start and Proportional Rate Reduction.
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* o Add toggle for shadow window mechanism. Suggested by David Hayes.
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* o Add toggle for non-congestion loss tolerance.
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* o Scaling parameter G is changed to a backoff factor;
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* conversion is given by: backoff_factor = 1000/(G * window).
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* o Limit shadow window to 2 * cwnd, or to cwnd when application limited.
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* o More accurate e^-x.
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*/
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#include <linux/kernel.h>
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#include <linux/random.h>
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#include <linux/module.h>
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#include <linux/sched/clock.h>
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#include <net/tcp.h>
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#define HYSTART_ACK_TRAIN 1
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#define HYSTART_DELAY 2
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static int window __read_mostly = 8;
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static unsigned int backoff_beta __read_mostly = 0.7071 * 1024; /* sqrt 0.5 */
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static unsigned int backoff_factor __read_mostly = 42;
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static unsigned int hystart_detect __read_mostly = 3;
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static unsigned int use_ineff __read_mostly = 5;
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static bool use_shadow __read_mostly = true;
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static bool use_tolerance __read_mostly;
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module_param(window, int, 0444);
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MODULE_PARM_DESC(window, "gradient window size (power of two <= 256)");
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module_param(backoff_beta, uint, 0644);
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MODULE_PARM_DESC(backoff_beta, "backoff beta (0-1024)");
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module_param(backoff_factor, uint, 0644);
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MODULE_PARM_DESC(backoff_factor, "backoff probability scale factor");
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module_param(hystart_detect, uint, 0644);
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MODULE_PARM_DESC(hystart_detect, "use Hybrid Slow start "
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"(0: disabled, 1: ACK train, 2: delay threshold, 3: both)");
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module_param(use_ineff, uint, 0644);
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MODULE_PARM_DESC(use_ineff, "use ineffectual backoff detection (threshold)");
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module_param(use_shadow, bool, 0644);
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MODULE_PARM_DESC(use_shadow, "use shadow window heuristic");
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module_param(use_tolerance, bool, 0644);
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MODULE_PARM_DESC(use_tolerance, "use loss tolerance heuristic");
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struct cdg_minmax {
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union {
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struct {
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s32 min;
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s32 max;
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};
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u64 v64;
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};
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};
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enum cdg_state {
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CDG_UNKNOWN = 0,
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CDG_NONFULL = 1,
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CDG_FULL = 2,
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CDG_BACKOFF = 3,
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};
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struct cdg {
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struct cdg_minmax rtt;
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struct cdg_minmax rtt_prev;
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struct cdg_minmax *gradients;
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struct cdg_minmax gsum;
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bool gfilled;
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u8 tail;
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u8 state;
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u8 delack;
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u32 rtt_seq;
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u32 shadow_wnd;
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u16 backoff_cnt;
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u16 sample_cnt;
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s32 delay_min;
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u32 last_ack;
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u32 round_start;
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};
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/**
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* nexp_u32 - negative base-e exponential
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* @ux: x in units of micro
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*
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* Returns exp(ux * -1e-6) * U32_MAX.
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*/
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static u32 __pure nexp_u32(u32 ux)
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{
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static const u16 v[] = {
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/* exp(-x)*65536-1 for x = 0, 0.000256, 0.000512, ... */
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65535,
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65518, 65501, 65468, 65401, 65267, 65001, 64470, 63422,
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61378, 57484, 50423, 38795, 22965, 8047, 987, 14,
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};
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u32 msb = ux >> 8;
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u32 res;
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int i;
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/* Cut off when ux >= 2^24 (actual result is <= 222/U32_MAX). */
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if (msb > U16_MAX)
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return 0;
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/* Scale first eight bits linearly: */
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res = U32_MAX - (ux & 0xff) * (U32_MAX / 1000000);
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/* Obtain e^(x + y + ...) by computing e^x * e^y * ...: */
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for (i = 1; msb; i++, msb >>= 1) {
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u32 y = v[i & -(msb & 1)] + U32_C(1);
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res = ((u64)res * y) >> 16;
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}
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return res;
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}
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/* Based on the HyStart algorithm (by Ha et al.) that is implemented in
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* tcp_cubic. Differences/experimental changes:
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* o Using Hayes' delayed ACK filter.
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* o Using a usec clock for the ACK train.
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* o Reset ACK train when application limited.
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* o Invoked at any cwnd (i.e. also when cwnd < 16).
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* o Invoked only when cwnd < ssthresh (i.e. not when cwnd == ssthresh).
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*/
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static void tcp_cdg_hystart_update(struct sock *sk)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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ca->delay_min = min_not_zero(ca->delay_min, ca->rtt.min);
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if (ca->delay_min == 0)
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return;
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if (hystart_detect & HYSTART_ACK_TRAIN) {
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u32 now_us = tp->tcp_mstamp;
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if (ca->last_ack == 0 || !tcp_is_cwnd_limited(sk)) {
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ca->last_ack = now_us;
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ca->round_start = now_us;
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} else if (before(now_us, ca->last_ack + 3000)) {
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u32 base_owd = max(ca->delay_min / 2U, 125U);
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ca->last_ack = now_us;
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if (after(now_us, ca->round_start + base_owd)) {
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTTRAINDETECT);
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NET_ADD_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTTRAINCWND,
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tcp_snd_cwnd(tp));
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tp->snd_ssthresh = tcp_snd_cwnd(tp);
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return;
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}
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}
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}
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if (hystart_detect & HYSTART_DELAY) {
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if (ca->sample_cnt < 8) {
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ca->sample_cnt++;
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} else {
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s32 thresh = max(ca->delay_min + ca->delay_min / 8U,
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125U);
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if (ca->rtt.min > thresh) {
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTDELAYDETECT);
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NET_ADD_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTDELAYCWND,
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tcp_snd_cwnd(tp));
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tp->snd_ssthresh = tcp_snd_cwnd(tp);
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}
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}
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}
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}
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static s32 tcp_cdg_grad(struct cdg *ca)
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{
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s32 gmin = ca->rtt.min - ca->rtt_prev.min;
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s32 gmax = ca->rtt.max - ca->rtt_prev.max;
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s32 grad;
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if (ca->gradients) {
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ca->gsum.min += gmin - ca->gradients[ca->tail].min;
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ca->gsum.max += gmax - ca->gradients[ca->tail].max;
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ca->gradients[ca->tail].min = gmin;
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ca->gradients[ca->tail].max = gmax;
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ca->tail = (ca->tail + 1) & (window - 1);
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gmin = ca->gsum.min;
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gmax = ca->gsum.max;
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}
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/* We keep sums to ignore gradients during cwnd reductions;
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* the paper's smoothed gradients otherwise simplify to:
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* (rtt_latest - rtt_oldest) / window.
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*
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* We also drop division by window here.
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*/
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grad = gmin > 0 ? gmin : gmax;
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/* Extrapolate missing values in gradient window: */
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if (!ca->gfilled) {
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if (!ca->gradients && window > 1)
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grad *= window; /* Memory allocation failed. */
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else if (ca->tail == 0)
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ca->gfilled = true;
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else
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grad = (grad * window) / (int)ca->tail;
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}
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/* Backoff was effectual: */
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if (gmin <= -32 || gmax <= -32)
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ca->backoff_cnt = 0;
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if (use_tolerance) {
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/* Reduce small variations to zero: */
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gmin = DIV_ROUND_CLOSEST(gmin, 64);
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gmax = DIV_ROUND_CLOSEST(gmax, 64);
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if (gmin > 0 && gmax <= 0)
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ca->state = CDG_FULL;
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else if ((gmin > 0 && gmax > 0) || gmax < 0)
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ca->state = CDG_NONFULL;
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}
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return grad;
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}
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static bool tcp_cdg_backoff(struct sock *sk, u32 grad)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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if (get_random_u32() <= nexp_u32(grad * backoff_factor))
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return false;
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if (use_ineff) {
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ca->backoff_cnt++;
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if (ca->backoff_cnt > use_ineff)
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return false;
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}
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ca->shadow_wnd = max(ca->shadow_wnd, tcp_snd_cwnd(tp));
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ca->state = CDG_BACKOFF;
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tcp_enter_cwr(sk);
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return true;
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}
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/* Not called in CWR or Recovery state. */
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static void tcp_cdg_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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u32 prior_snd_cwnd;
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u32 incr;
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if (tcp_in_slow_start(tp) && hystart_detect)
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tcp_cdg_hystart_update(sk);
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if (after(ack, ca->rtt_seq) && ca->rtt.v64) {
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s32 grad = 0;
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if (ca->rtt_prev.v64)
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grad = tcp_cdg_grad(ca);
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ca->rtt_seq = tp->snd_nxt;
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ca->rtt_prev = ca->rtt;
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ca->rtt.v64 = 0;
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ca->last_ack = 0;
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ca->sample_cnt = 0;
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if (grad > 0 && tcp_cdg_backoff(sk, grad))
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return;
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}
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if (!tcp_is_cwnd_limited(sk)) {
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ca->shadow_wnd = min(ca->shadow_wnd, tcp_snd_cwnd(tp));
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return;
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}
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prior_snd_cwnd = tcp_snd_cwnd(tp);
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tcp_reno_cong_avoid(sk, ack, acked);
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incr = tcp_snd_cwnd(tp) - prior_snd_cwnd;
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ca->shadow_wnd = max(ca->shadow_wnd, ca->shadow_wnd + incr);
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}
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static void tcp_cdg_acked(struct sock *sk, const struct ack_sample *sample)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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if (sample->rtt_us <= 0)
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return;
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/* A heuristic for filtering delayed ACKs, adapted from:
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* D.A. Hayes. "Timing enhancements to the FreeBSD kernel to support
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* delay and rate based TCP mechanisms." TR 100219A. CAIA, 2010.
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*/
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if (tp->sacked_out == 0) {
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if (sample->pkts_acked == 1 && ca->delack) {
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/* A delayed ACK is only used for the minimum if it is
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* provenly lower than an existing non-zero minimum.
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*/
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ca->rtt.min = min(ca->rtt.min, sample->rtt_us);
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ca->delack--;
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return;
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} else if (sample->pkts_acked > 1 && ca->delack < 5) {
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ca->delack++;
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}
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}
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ca->rtt.min = min_not_zero(ca->rtt.min, sample->rtt_us);
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ca->rtt.max = max(ca->rtt.max, sample->rtt_us);
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}
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static u32 tcp_cdg_ssthresh(struct sock *sk)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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if (ca->state == CDG_BACKOFF)
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return max(2U, (tcp_snd_cwnd(tp) * min(1024U, backoff_beta)) >> 10);
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if (ca->state == CDG_NONFULL && use_tolerance)
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return tcp_snd_cwnd(tp);
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ca->shadow_wnd = min(ca->shadow_wnd >> 1, tcp_snd_cwnd(tp));
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if (use_shadow)
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return max3(2U, ca->shadow_wnd, tcp_snd_cwnd(tp) >> 1);
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return max(2U, tcp_snd_cwnd(tp) >> 1);
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}
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static void tcp_cdg_cwnd_event(struct sock *sk, const enum tcp_ca_event ev)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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struct cdg_minmax *gradients;
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switch (ev) {
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case CA_EVENT_CWND_RESTART:
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gradients = ca->gradients;
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if (gradients)
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memset(gradients, 0, window * sizeof(gradients[0]));
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memset(ca, 0, sizeof(*ca));
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ca->gradients = gradients;
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ca->rtt_seq = tp->snd_nxt;
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ca->shadow_wnd = tcp_snd_cwnd(tp);
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break;
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case CA_EVENT_COMPLETE_CWR:
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ca->state = CDG_UNKNOWN;
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ca->rtt_seq = tp->snd_nxt;
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ca->rtt_prev = ca->rtt;
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ca->rtt.v64 = 0;
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break;
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default:
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break;
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}
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}
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static void tcp_cdg_init(struct sock *sk)
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{
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struct cdg *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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ca->gradients = NULL;
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/* We silently fall back to window = 1 if allocation fails. */
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if (window > 1)
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ca->gradients = kcalloc(window, sizeof(ca->gradients[0]),
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GFP_NOWAIT | __GFP_NOWARN);
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ca->rtt_seq = tp->snd_nxt;
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ca->shadow_wnd = tcp_snd_cwnd(tp);
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}
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static void tcp_cdg_release(struct sock *sk)
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{
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struct cdg *ca = inet_csk_ca(sk);
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kfree(ca->gradients);
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ca->gradients = NULL;
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}
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static struct tcp_congestion_ops tcp_cdg __read_mostly = {
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.cong_avoid = tcp_cdg_cong_avoid,
|
|
.cwnd_event = tcp_cdg_cwnd_event,
|
|
.pkts_acked = tcp_cdg_acked,
|
|
.undo_cwnd = tcp_reno_undo_cwnd,
|
|
.ssthresh = tcp_cdg_ssthresh,
|
|
.release = tcp_cdg_release,
|
|
.init = tcp_cdg_init,
|
|
.owner = THIS_MODULE,
|
|
.name = "cdg",
|
|
};
|
|
|
|
static int __init tcp_cdg_register(void)
|
|
{
|
|
if (backoff_beta > 1024 || window < 1 || window > 256)
|
|
return -ERANGE;
|
|
if (!is_power_of_2(window))
|
|
return -EINVAL;
|
|
|
|
BUILD_BUG_ON(sizeof(struct cdg) > ICSK_CA_PRIV_SIZE);
|
|
tcp_register_congestion_control(&tcp_cdg);
|
|
return 0;
|
|
}
|
|
|
|
static void __exit tcp_cdg_unregister(void)
|
|
{
|
|
tcp_unregister_congestion_control(&tcp_cdg);
|
|
}
|
|
|
|
module_init(tcp_cdg_register);
|
|
module_exit(tcp_cdg_unregister);
|
|
MODULE_AUTHOR("Kenneth Klette Jonassen");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_DESCRIPTION("TCP CDG");
|