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Commit 8a9c7e92 authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[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: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8995a238

net/dccp/ccids/lib/loss_interval.c

+156 −5
Original line number Diff line number Diff line 
/*

 *  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",

net/dccp/ccids/lib/loss_interval.h

+55 −1
Original line number Diff line number Diff line
@@ -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);

net/dccp/ccids/lib/packet_history.c

+214 −4
Original line number Diff line number Diff line
@@ -151,11 +151,10 @@ void tfrc_rx_packet_history_exit(void) 
	}

}



void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,

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;

net/dccp/ccids/lib/packet_history.h

+7 −4
Original line number Diff line number Diff line
@@ -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);

net/dccp/ccids/lib/tfrc.h

+3 −0
Original line number Diff line number Diff line
@@ -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;