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/*
* Ouroboros - Copyright (C) 2016 - 2024
*
* Multi-bit ECN Congestion Avoidance
*
* Dimitri Staessens <dimitri@ouroboros.rocks>
* Sander Vrijders <sander@ouroboros.rocks>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., http://www.fsf.org/about/contact/.
*/
#if defined(__linux__) || defined(__CYGWIN__)
#define _DEFAULT_SOURCE
#else
#define _POSIX_C_SOURCE 200809L
#endif
#include "config.h"
#include <ouroboros/ipcp-dev.h>
#include <ouroboros/time.h>
#include "mb-ecn.h"
#include <inttypes.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
/* congestion avoidance constants */
#define CA_SHFT 5 /* Average over 32 pkts */
#define CA_WND (1 << CA_SHFT) /* 32 pkts receiver wnd */
#define CA_UPD (1 << (CA_SHFT - 2)) /* Update snd every 8 pkt */
#define CA_SLOT 24 /* Initial slot = 16 ms */
#define CA_INC 1UL << 16 /* ~4MiB/s^2 additive inc */
#define CA_IWL 1UL << 16 /* Initial limit ~4MiB/s */
#define CA_MINPS 8 /* Mimimum pkts / slot */
#define CA_MAXPS 64 /* Maximum pkts / slot */
#define ECN_Q_SHFT 4
#define ts_to_ns(ts) ((size_t) ts.tv_sec * BILLION + ts.tv_nsec)
struct mb_ecn_ctx {
uint16_t rx_ece; /* Level of congestion (upstream) */
size_t rx_ctr; /* Receiver side packet counter */
uint16_t tx_ece; /* Level of congestion (downstream) */
size_t tx_ctr; /* Sender side packet counter */
size_t tx_wbc; /* Window byte count */
size_t tx_wpc; /* Window packet count */
size_t tx_wbl; /* Window byte limit */
bool tx_cav; /* Congestion avoidance */
size_t tx_mul; /* Slot size multiplier */
size_t tx_inc; /* Additive increase */
size_t tx_slot;
};
struct ca_ops mb_ecn_ca_ops = {
.ctx_create = mb_ecn_ctx_create,
.ctx_destroy = mb_ecn_ctx_destroy,
.ctx_update_snd = mb_ecn_ctx_update_snd,
.ctx_update_rcv = mb_ecn_ctx_update_rcv,
.ctx_update_ece = mb_ecn_ctx_update_ece,
.wnd_wait = mb_ecn_wnd_wait,
.calc_ecn = mb_ecn_calc_ecn,
.print_stats = mb_ecn_print_stats
};
void * mb_ecn_ctx_create(void)
{
struct timespec now;
struct mb_ecn_ctx * ctx;
ctx = malloc(sizeof(*ctx));
if (ctx == NULL)
return NULL;
clock_gettime(PTHREAD_COND_CLOCK, &now);
memset(ctx, 0, sizeof(*ctx));
ctx->tx_mul = CA_SLOT;
ctx->tx_wbl = CA_IWL;
ctx->tx_inc = CA_INC;
ctx->tx_slot = ts_to_ns(now) >> ctx->tx_mul;
return (void *) ctx;
}
void mb_ecn_ctx_destroy(void * ctx)
{
free(ctx);
}
#define _slot_after(new, old) ((int64_t) (old - new) < 0)
ca_wnd_t mb_ecn_ctx_update_snd(void * _ctx,
size_t len)
{
struct timespec now;
size_t slot;
ca_wnd_t wnd;
struct mb_ecn_ctx * ctx = _ctx;
clock_gettime(PTHREAD_COND_CLOCK, &now);
slot = ts_to_ns(now) >> ctx->tx_mul;
ctx->tx_ctr++;
ctx->tx_wpc++;
ctx->tx_wbc += len;
if (ctx->tx_ctr > CA_WND)
ctx->tx_ece = 0;
if (_slot_after(slot, ctx->tx_slot)) {
bool carry = false; /* may carry over if window increases */
ctx->tx_slot = slot;
if (!ctx->tx_cav) { /* Slow start */
if (ctx->tx_wbc > ctx->tx_wbl)
ctx->tx_wbl <<= 1;
} else {
if (ctx->tx_ece) /* Mult. Decrease */
ctx->tx_wbl -= (ctx->tx_wbl * ctx->tx_ece)
>> (CA_SHFT + 8);
else /* Add. Increase */
ctx->tx_wbl = ctx->tx_wbc + ctx->tx_inc;
}
/* Window scaling */
if (ctx->tx_wpc < CA_MINPS) {
size_t fact = 0; /* factor to scale the window up */
size_t pkts = ctx->tx_wpc;
while (pkts < CA_MINPS) {
pkts <<= 1;
fact++;
}
ctx->tx_mul += fact;
ctx->tx_slot >>= fact;
if ((ctx->tx_slot & ((1 << fact) - 1)) == 0) {
carry = true;
ctx->tx_slot += 1;
}
ctx->tx_wbl <<= fact;
ctx->tx_inc <<= fact;
} else if (ctx->tx_wpc > CA_MAXPS) {
size_t fact = 0; /* factor to scale the window down */
size_t pkts = ctx->tx_wpc;
while (pkts > CA_MAXPS) {
pkts >>= 1;
fact++;
}
ctx->tx_mul -= fact;
ctx->tx_slot <<= fact;
ctx->tx_wbl >>= fact;
ctx->tx_inc >>= fact;
} else {
ctx->tx_slot = slot;
}
if (!carry) {
ctx->tx_wbc = 0;
ctx->tx_wpc = 0;
}
}
if (ctx->tx_wbc > ctx->tx_wbl)
wnd.wait = ((ctx->tx_slot + 1) << ctx->tx_mul) - ts_to_ns(now);
else
wnd.wait = 0;
return wnd;
}
void mb_ecn_wnd_wait(ca_wnd_t wnd)
{
if (wnd.wait > 0) {
struct timespec s = TIMESPEC_INIT_S(0);
if (wnd.wait > BILLION) /* Don't care throttling < 1s */
s.tv_sec = 1;
else
s.tv_nsec = wnd.wait;
nanosleep(&s, NULL);
}
}
bool mb_ecn_ctx_update_rcv(void * _ctx,
size_t len,
uint8_t ecn,
uint16_t * ece)
{
struct mb_ecn_ctx* ctx = _ctx;
bool update;
(void) len;
if ((ctx->rx_ece | ecn) == 0)
return false;
if (ecn == 0) { /* End of congestion */
ctx->rx_ece >>= 2;
update = ctx->rx_ece == 0;
} else {
if (ctx->rx_ece == 0) { /* Start of congestion */
ctx->rx_ece = ecn;
ctx->rx_ctr = 0;
update = true;
} else { /* Congestion update */
ctx->rx_ece -= ctx->rx_ece >> CA_SHFT;
ctx->rx_ece += ecn;
update = (ctx->rx_ctr++ & (CA_UPD - 1)) == true;
}
}
*ece = ctx->rx_ece;
return update;
}
void mb_ecn_ctx_update_ece(void * _ctx,
uint16_t ece)
{
struct mb_ecn_ctx* ctx = _ctx;
ctx->tx_ece = ece;
ctx->tx_ctr = 0;
ctx->tx_cav = true;
}
int mb_ecn_calc_ecn(int fd,
uint8_t * ecn,
qoscube_t qc,
size_t len)
{
size_t q;
(void) len;
(void) qc;
q = ipcp_flow_queued(fd);
*ecn |= (uint8_t) (q >> ECN_Q_SHFT);
return 0;
}
ssize_t mb_ecn_print_stats(void * _ctx,
char * buf,
size_t len)
{
struct mb_ecn_ctx* ctx = _ctx;
char * regime;
if (len < 1024)
return 0;
if (!ctx->tx_cav)
regime = "Slow start";
else if (ctx->tx_ece)
regime = "Multiplicative dec";
else
regime = "Additive inc";
sprintf(buf,
"Congestion avoidance algorithm: %20s\n"
"Upstream congestion level: %20u\n"
"Upstream packet counter: %20zu\n"
"Downstream congestion level: %20u\n"
"Downstream packet counter: %20zu\n"
"Congestion window size (ns): %20" PRIu64 "\n"
"Packets in this window: %20zu\n"
"Bytes in this window: %20zu\n"
"Max bytes in this window: %20zu\n"
"Current congestion regime: %20s\n",
"Multi-bit ECN",
ctx->tx_ece, ctx->tx_ctr,
ctx->rx_ece, ctx->rx_ctr, (uint64_t) (1ULL << ctx->tx_mul),
ctx->tx_wpc, ctx->tx_wbc, ctx->tx_wbl,
regime);
return strlen(buf);
}
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