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[TFRC]: Ringbuffer to track loss interval history 

A ringbuffer-based implementation of loss interval history is easier to
maintain, allocate, and update.

The `swap' routine to keep the RX history sorted is due to and was written
by Arnaldo Carvalho de Melo, simplifying an earlier macro-based variant.

Details:
 * access to the Loss Interval Records via macro wrappers (with safety checks);
 * simplified, on-demand allocation of entries (no extra memory consumption on
   lossless links); cache allocation is local to the module / exported as service;
 * provision of RFC-compliant algorithm to re-compute average loss interval;
 * provision of comprehensive, new loss detection algorithm
 	- support for all cases of loss, including re-ordered/duplicate packets;
 	- waiting for NDUPACK=3 packets to fill the hole;
	- updating loss records when a late-arriving packet fills a hole.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gerrit Renker 2007-12-12 13:50:51 -02:00 committed by David S. Miller
parent 8995a238ef
commit 8a9c7e92e0
5 changed files with 435 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

161
net/dccp/ccids/lib/loss_interval.c
View File

@ -1,6 +1,7 @@
/*
* net/dccp/ccids/lib/loss_interval.c
*
* Copyright (c) 2007 The University of Aberdeen, Scotland, UK
* Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
* Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
* Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
@ -10,12 +11,7 @@
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*/
#include <linux/module.h>
#include <net/sock.h>
#include "../../dccp.h"
#include "loss_interval.h"
#include "packet_history.h"
#include "tfrc.h"
#define DCCP_LI_HIST_IVAL_F_LENGTH 8
@ -27,6 +23,54 @@ struct dccp_li_hist_entry {
u32 dccplih_interval;
};
static struct kmem_cache *tfrc_lh_slab __read_mostly;
/* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
/* implements LIFO semantics on the array */
static inline u8 LIH_INDEX(const u8 ctr)
{
return (LIH_SIZE - 1 - (ctr % LIH_SIZE));
}
/* the `counter' index always points at the next entry to be populated */
static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
{
return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
}
/* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
{
BUG_ON(i >= lh->counter);
return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
}
/*
* On-demand allocation and de-allocation of entries
*/
static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
{
if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
GFP_ATOMIC);
return lh->ring[LIH_INDEX(lh->counter)];
}
void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
{
if (!tfrc_lh_is_initialised(lh))
return;
for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
kmem_cache_free(tfrc_lh_slab,
lh->ring[LIH_INDEX(lh->counter)]);
lh->ring[LIH_INDEX(lh->counter)] = NULL;
}
}
EXPORT_SYMBOL_GPL(tfrc_lh_cleanup);
static struct kmem_cache *dccp_li_cachep __read_mostly;
static inline struct dccp_li_hist_entry *dccp_li_hist_entry_new(const gfp_t prio)
@ -98,6 +142,65 @@ u32 dccp_li_hist_calc_i_mean(struct list_head *list)
EXPORT_SYMBOL_GPL(dccp_li_hist_calc_i_mean);
static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
{
u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */
for (i=0; i <= k; i++) {
i_i = tfrc_lh_get_interval(lh, i);
if (i < k) {
i_tot0 += i_i * tfrc_lh_weights[i];
w_tot += tfrc_lh_weights[i];
}
if (i > 0)
i_tot1 += i_i * tfrc_lh_weights[i-1];
}
BUG_ON(w_tot == 0);
lh->i_mean = max(i_tot0, i_tot1) / w_tot;
}
/**
* tfrc_lh_update_i_mean - Update the `open' loss interval I_0
* For recomputing p: returns `true' if p > p_prev <=> 1/p < 1/p_prev
*/
u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
{
struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
u32 old_i_mean = lh->i_mean;
s64 length;
if (cur == NULL) /* not initialised */
return 0;
length = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq);
if (length - cur->li_length <= 0) /* duplicate or reordered */
return 0;
if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
/*
* Implements RFC 4342, 10.2:
* If a packet S (skb) exists whose seqno comes `after' the one
* starting the current loss interval (cur) and if the modulo-16
* distance from C(cur) to C(S) is greater than 4, consider all
* subsequent packets as belonging to a new loss interval. This
* test is necessary since CCVal may wrap between intervals.
*/
cur->li_is_closed = 1;
if (tfrc_lh_length(lh) == 1) /* due to RFC 3448, 6.3.1 */
return 0;
cur->li_length = length;
tfrc_lh_calc_i_mean(lh);
return (lh->i_mean < old_i_mean);
}
EXPORT_SYMBOL_GPL(tfrc_lh_update_i_mean);
static int dccp_li_hist_interval_new(struct list_head *list,
const u64 seq_loss, const u8 win_loss)
{
@ -284,6 +387,54 @@ void dccp_li_update_li(struct sock *sk,
EXPORT_SYMBOL_GPL(dccp_li_update_li);
/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
struct tfrc_rx_hist_entry *new_loss)
{
return dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
(cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
}
/** tfrc_lh_interval_add - Insert new record into the Loss Interval database
* @lh: Loss Interval database
* @rh: Receive history containing a fresh loss event
* @calc_first_li: Caller-dependent routine to compute length of first interval
* @sk: Used by @calc_first_li in caller-specific way (subtyping)
* Updates I_mean and returns 1 if a new interval has in fact been added to @lh.
*/
int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
u32 (*calc_first_li)(struct sock *), struct sock *sk)
{
struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;
if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
return 0;
new = tfrc_lh_demand_next(lh);
if (unlikely(new == NULL)) {
DCCP_CRIT("Cannot allocate/add loss record.");
return 0;
}
new->li_seqno = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
new->li_ccval = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
new->li_is_closed = 0;
if (++lh->counter == 1)
lh->i_mean = new->li_length = (*calc_first_li)(sk);
else {
cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
new->li_length = dccp_delta_seqno(new->li_seqno,
tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno);
if (lh->counter > (2*LIH_SIZE))
lh->counter -= LIH_SIZE;
tfrc_lh_calc_i_mean(lh);
}
return 1;
}
EXPORT_SYMBOL_GPL(tfrc_lh_interval_add);
int __init dccp_li_init(void)
{
dccp_li_cachep = kmem_cache_create("dccp_li_hist",

56
net/dccp/ccids/lib/loss_interval.h
View File

@ -3,6 +3,7 @@
/*
* net/dccp/ccids/lib/loss_interval.h
*
* Copyright (c) 2007 The University of Aberdeen, Scotland, UK
* Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
* Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
* Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
@ -12,11 +13,64 @@
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*/
#include <linux/ktime.h>
#include <linux/list.h>
#include <linux/slab.h>
/*
* Number of loss intervals (RFC 4342, 8.6.1). The history size is one more than
* NINTERVAL, since the `open' interval I_0 is always stored as the first entry.
*/
#define NINTERVAL 8
#define LIH_SIZE (NINTERVAL + 1)
/**
* tfrc_loss_interval - Loss history record for TFRC-based protocols
* @li_seqno: Highest received seqno before the start of loss
* @li_ccval: The CCVal belonging to @li_seqno
* @li_is_closed: Whether @li_seqno is older than 1 RTT
* @li_length: Loss interval sequence length
*/
struct tfrc_loss_interval {
u64 li_seqno:48,
li_ccval:4,
li_is_closed:1;
u32 li_length;
};
/**
* tfrc_loss_hist - Loss record database
* @ring: Circular queue managed in LIFO manner
* @counter: Current count of entries (can be more than %LIH_SIZE)
* @i_mean: Current Average Loss Interval [RFC 3448, 5.4]
*/
struct tfrc_loss_hist {
struct tfrc_loss_interval *ring[LIH_SIZE];
u8 counter;
u32 i_mean;
};
static inline void tfrc_lh_init(struct tfrc_loss_hist *lh)
{
memset(lh, 0, sizeof(struct tfrc_loss_hist));
}
static inline u8 tfrc_lh_is_initialised(struct tfrc_loss_hist *lh)
{
return lh->counter > 0;
}
static inline u8 tfrc_lh_length(struct tfrc_loss_hist *lh)
{
return min(lh->counter, (u8)LIH_SIZE);
}
extern void dccp_li_hist_purge(struct list_head *list);
struct tfrc_rx_hist;
extern int tfrc_lh_interval_add(struct tfrc_loss_hist *, struct tfrc_rx_hist *,
u32 (*first_li)(struct sock *), struct sock *);
extern u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *);
extern void tfrc_lh_cleanup(struct tfrc_loss_hist *lh);
extern u32 dccp_li_hist_calc_i_mean(struct list_head *list);

218
net/dccp/ccids/lib/packet_history.c
View File

@ -151,11 +151,10 @@ void tfrc_rx_packet_history_exit(void)
}
}
void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
const struct sk_buff *skb,
const u32 ndp)
static inline void tfrc_rx_hist_entry_from_skb(struct tfrc_rx_hist_entry *entry,
const struct sk_buff *skb,
const u32 ndp)
{
struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);
const struct dccp_hdr *dh = dccp_hdr(skb);
entry->tfrchrx_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
@ -164,6 +163,15 @@ void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
entry->tfrchrx_ndp = ndp;
entry->tfrchrx_tstamp = ktime_get_real();
}
void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
const struct sk_buff *skb,
const u32 ndp)
{
struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);
tfrc_rx_hist_entry_from_skb(entry, skb, ndp);
}
EXPORT_SYMBOL_GPL(tfrc_rx_hist_add_packet);
/* has the packet contained in skb been seen before? */
@ -209,6 +217,208 @@ int tfrc_rx_hist_new_loss_indicated(struct tfrc_rx_hist *h,
}
EXPORT_SYMBOL_GPL(tfrc_rx_hist_new_loss_indicated);
static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)
{
const u8 idx_a = tfrc_rx_hist_index(h, a),
idx_b = tfrc_rx_hist_index(h, b);
struct tfrc_rx_hist_entry *tmp = h->ring[idx_a];
h->ring[idx_a] = h->ring[idx_b];
h->ring[idx_b] = tmp;
}
/*
* Private helper functions for loss detection.
*
* In the descriptions, `Si' refers to the sequence number of entry number i,
* whose NDP count is `Ni' (lower case is used for variables).
* Note: All __after_loss functions expect that a test against duplicates has
* been performed already: the seqno of the skb must not be less than the
* seqno of loss_prev; and it must not equal that of any valid hist_entry.
*/
static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2)
{
u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
s2 = DCCP_SKB_CB(skb)->dccpd_seq;
int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
d12 = dccp_delta_seqno(s1, s2), d2;
if (d12 > 0) { /* S1 < S2 */
h->loss_count = 2;
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);
return;
}
/* S0 < S2 < S1 */
d2 = dccp_delta_seqno(s0, s2);
if (d2 == 1 || n2 >= d2) { /* S2 is direct successor of S0 */
int d21 = -d12;
if (d21 == 1 || n1 >= d21) {
/* hole is filled: S0, S2, and S1 are consecutive */
h->loss_count = 0;
h->loss_start = tfrc_rx_hist_index(h, 1);
} else
/* gap between S2 and S1: just update loss_prev */
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);
} else { /* hole between S0 and S2 */
/*
* Reorder history to insert S2 between S0 and s1
*/
tfrc_rx_hist_swap(h, 0, 3);
h->loss_start = tfrc_rx_hist_index(h, 3);
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n2);
h->loss_count = 2;
}
}
/* return 1 if a new loss event has been identified */
static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
{
u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
s3 = DCCP_SKB_CB(skb)->dccpd_seq;
int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
d23 = dccp_delta_seqno(s2, s3), d13, d3, d31;
if (d23 > 0) { /* S2 < S3 */
h->loss_count = 3;
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);
return 1;
}
/* S3 < S2 */
d13 = dccp_delta_seqno(s1, s3);
if (d13 > 0) {
/*
* The sequence number order is S1, S3, S2
* Reorder history to insert entry between S1 and S2
*/
tfrc_rx_hist_swap(h, 2, 3);
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
h->loss_count = 3;
return 1;
}
/* S0 < S3 < S1 */
d31 = -d13;
d3 = dccp_delta_seqno(s0, s3);
if (d3 == 1 || n3 >= d3) { /* S3 is a successor of S0 */
if (d31 == 1 || n1 >= d31) {
/* hole between S0 and S1 filled by S3 */
int d2 = dccp_delta_seqno(s1, s2),
n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;
if (d2 == 1 || n2 >= d2) {
/* entire hole filled by S0, S3, S1, S2 */
h->loss_start = tfrc_rx_hist_index(h, 2);
h->loss_count = 0;
} else {
/* gap remains between S1 and S2 */
h->loss_start = tfrc_rx_hist_index(h, 1);
h->loss_count = 1;
}
} else /* gap exists between S3 and S1, loss_count stays at 2 */
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n3);
return 0;
}
/*
* The remaining case: S3 is not a successor of S0.
* Sequence order is S0, S3, S1, S2; reorder to insert between S0 and S1
*/
tfrc_rx_hist_swap(h, 0, 3);
h->loss_start = tfrc_rx_hist_index(h, 3);
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n3);
h->loss_count = 3;
return 1;
}
/* return the signed modulo-2^48 sequence number distance from entry e1 to e2 */
static s64 tfrc_rx_hist_delta_seqno(struct tfrc_rx_hist *h, u8 e1, u8 e2)
{
DCCP_BUG_ON(e1 > h->loss_count || e2 > h->loss_count);
return dccp_delta_seqno(tfrc_rx_hist_entry(h, e1)->tfrchrx_seqno,
tfrc_rx_hist_entry(h, e2)->tfrchrx_seqno);
}
/* recycle RX history records to continue loss detection if necessary */
static void __three_after_loss(struct tfrc_rx_hist *h)
{
/*
* The distance between S0 and S1 is always greater than 1 and the NDP
* count of S1 is smaller than this distance. Otherwise there would
* have been no loss. Hence it is only necessary to see whether there
* are further missing data packets between S1/S2 and S2/S3.
*/
int d2 = tfrc_rx_hist_delta_seqno(h, 1, 2),
d3 = tfrc_rx_hist_delta_seqno(h, 2, 3),
n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;
if (d2 == 1 || n2 >= d2) { /* S2 is successor to S1 */
if (d3 == 1 || n3 >= d3) {
/* S3 is successor of S2: entire hole is filled */
h->loss_start = tfrc_rx_hist_index(h, 3);
h->loss_count = 0;
} else {
/* gap between S2 and S3 */
h->loss_start = tfrc_rx_hist_index(h, 2);
h->loss_count = 1;
}
} else { /* gap between S1 and S2 */
h->loss_start = tfrc_rx_hist_index(h, 1);
h->loss_count = 2;
}
}
/**
* tfrc_rx_handle_loss - Loss detection and further processing
* @h: The non-empty RX history object
* @lh: Loss Intervals database to update
* @skb: Currently received packet
* @ndp: The NDP count belonging to @skb
* @calc_first_li: Caller-dependent computation of first loss interval in @lh
* @sk: Used by @calc_first_li (see tfrc_lh_interval_add)
* Chooses action according to pending loss, updates LI database when a new
* loss was detected, and does required post-processing. Returns 1 when caller
* should send feedback, 0 otherwise.
*/
int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
struct tfrc_loss_hist *lh,
struct sk_buff *skb, u32 ndp,
u32 (*calc_first_li)(struct sock *), struct sock *sk)
{
int is_new_loss = 0;
if (h->loss_count == 1) {
__one_after_loss(h, skb, ndp);
} else if (h->loss_count != 2) {
DCCP_BUG("invalid loss_count %d", h->loss_count);
} else if (__two_after_loss(h, skb, ndp)) {
/*
* Update Loss Interval database and recycle RX records
*/
is_new_loss = tfrc_lh_interval_add(lh, h, calc_first_li, sk);
__three_after_loss(h);
}
return is_new_loss;
}
EXPORT_SYMBOL_GPL(tfrc_rx_handle_loss);
int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)
{
int i;

11
net/dccp/ccids/lib/packet_history.h
View File

@ -36,10 +36,9 @@
#ifndef _DCCP_PKT_HIST_
#define _DCCP_PKT_HIST_
#include <linux/ktime.h>
#include <linux/types.h>
struct sk_buff;
#include <linux/list.h>
#include <linux/slab.h>
#include "tfrc.h"
struct tfrc_tx_hist_entry;
@ -125,6 +124,10 @@ extern void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
extern int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb);
extern int tfrc_rx_hist_new_loss_indicated(struct tfrc_rx_hist *h,
const struct sk_buff *skb, u32 ndp);
struct tfrc_loss_hist;
extern int tfrc_rx_handle_loss(struct tfrc_rx_hist *, struct tfrc_loss_hist *,
struct sk_buff *skb, u32 ndp,
u32 (*first_li)(struct sock *), struct sock *);
extern u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h,
const struct sk_buff *skb);
extern int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h);

3
net/dccp/ccids/lib/tfrc.h
View File

@ -17,6 +17,9 @@
#include <linux/types.h>
#include <asm/div64.h>
#include "../../dccp.h"
/* internal includes that this module exports: */
#include "loss_interval.h"
#include "packet_history.h"
#ifdef CONFIG_IP_DCCP_TFRC_DEBUG
extern int tfrc_debug;