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freebsd-skq/sys/netinet/tcp_sack.c
Richard Scheffenegger 0471a8c734 tcp: SACK Lost Retransmission Detection (LRD) 
Recover from excessive losses without reverting to a
retransmission timeout (RTO). Disabled by default, enable
with sysctl net.inet.tcp.do_lrd=1

Reviewed By: #transport, rrs, tuexen, #manpages
Sponsored by: Netapp, Inc.
Differential Revision: https://reviews.freebsd.org/D28931
2021-05-10 19:06:20 +02:00

1053 lines
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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
* The Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)tcp_sack.c 8.12 (Berkeley) 5/24/95
*/
/*-
* @@(#)COPYRIGHT 1.1 (NRL) 17 January 1995
*
* NRL grants permission for redistribution and use in source and binary
* forms, with or without modification, of the software and documentation
* created at NRL provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgements:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* This product includes software developed at the Information
* Technology Division, US Naval Research Laboratory.
* 4. Neither the name of the NRL nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
* IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* The views and conclusions contained in the software and documentation
* are those of the authors and should not be interpreted as representing
* official policies, either expressed or implied, of the US Naval
* Research Laboratory (NRL).
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_tcpdebug.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/proc.h> /* for proc0 declaration */
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
#include <vm/uma.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/route.h>
#include <net/vnet.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_var.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet6/tcp6_var.h>
#include <netinet/tcpip.h>
#include <netinet/cc/cc.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif /* TCPDEBUG */
#include <machine/in_cksum.h>
VNET_DECLARE(struct uma_zone *, sack_hole_zone);
#define V_sack_hole_zone VNET(sack_hole_zone)
SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
"TCP SACK");
VNET_DEFINE(int, tcp_do_sack) = 1;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_sack), 0,
"Enable/Disable TCP SACK support");
VNET_DEFINE(int, tcp_do_newsack) = 1;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_newsack), 0,
"Use revised SACK loss recovery per RFC 6675");
VNET_DEFINE(int, tcp_sack_maxholes) = 128;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_sack_maxholes), 0,
"Maximum number of TCP SACK holes allowed per connection");
VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_sack_globalmaxholes), 0,
"Global maximum number of TCP SACK holes");
VNET_DEFINE(int, tcp_sack_globalholes) = 0;
SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
&VNET_NAME(tcp_sack_globalholes), 0,
"Global number of TCP SACK holes currently allocated");
int
tcp_dsack_block_exists(struct tcpcb *tp)
{
/* Return true if a DSACK block exists */
if (tp->rcv_numsacks == 0)
return (0);
if (SEQ_LEQ(tp->sackblks[0].end, tp->rcv_nxt))
return(1);
return (0);
}
/*
* This function will find overlaps with the currently stored sackblocks
* and add any overlap as a dsack block upfront
*/
void
tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
{
struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
int i, j, n, identical;
tcp_seq start, end;
INP_WLOCK_ASSERT(tp->t_inpcb);
KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
((rcv_end == tp->rcv_nxt) &&
(tp->rcv_numsacks > 0 ) &&
(tp->sackblks[0].end == tp->rcv_nxt))) {
saved_blks[0].start = rcv_start;
saved_blks[0].end = rcv_end;
} else {
saved_blks[0].start = saved_blks[0].end = 0;
}
head_blk.start = head_blk.end = 0;
mid_blk.start = rcv_start;
mid_blk.end = rcv_end;
identical = 0;
for (i = 0; i < tp->rcv_numsacks; i++) {
start = tp->sackblks[i].start;
end = tp->sackblks[i].end;
if (SEQ_LT(rcv_end, start)) {
/* pkt left to sack blk */
continue;
}
if (SEQ_GT(rcv_start, end)) {
/* pkt right to sack blk */
continue;
}
if (SEQ_GT(tp->rcv_nxt, end)) {
if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
(SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
(head_blk.start == head_blk.end))) {
head_blk.start = SEQ_MAX(rcv_start, start);
head_blk.end = SEQ_MIN(rcv_end, end);
}
continue;
}
if (((head_blk.start == head_blk.end) ||
SEQ_LT(start, head_blk.start)) &&
(SEQ_GT(end, rcv_start) &&
SEQ_LEQ(start, rcv_end))) {
head_blk.start = start;
head_blk.end = end;
}
mid_blk.start = SEQ_MIN(mid_blk.start, start);
mid_blk.end = SEQ_MAX(mid_blk.end, end);
if ((mid_blk.start == start) &&
(mid_blk.end == end))
identical = 1;
}
if (SEQ_LT(head_blk.start, head_blk.end)) {
/* store overlapping range */
saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
saved_blks[0].end = SEQ_MIN(rcv_end, head_blk.end);
}
n = 1;
/*
* Second, if not ACKed, store the SACK block that
* overlaps with the DSACK block unless it is identical
*/
if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
!((mid_blk.start == saved_blks[0].start) &&
(mid_blk.end == saved_blks[0].end))) ||
identical == 1) {
saved_blks[n].start = mid_blk.start;
saved_blks[n++].end = mid_blk.end;
}
for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
(SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
saved_blks[n++] = tp->sackblks[j];
}
j = 0;
for (i = 0; i < n; i++) {
/* we can end up with a stale initial entry */
if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
tp->sackblks[j++] = saved_blks[i];
}
}
tp->rcv_numsacks = j;
}
/*
* This function is called upon receipt of new valid data (while not in
* header prediction mode), and it updates the ordered list of sacks.
*/
void
tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
{
/*
* First reported block MUST be the most recent one. Subsequent
* blocks SHOULD be in the order in which they arrived at the
* receiver. These two conditions make the implementation fully
* compliant with RFC 2018.
*/
struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
int num_head, num_saved, i;
INP_WLOCK_ASSERT(tp->t_inpcb);
/* Check arguments. */
KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
if ((rcv_start == rcv_end) &&
(tp->rcv_numsacks >= 1) &&
(rcv_end == tp->sackblks[0].end)) {
/* retaining DSACK block below rcv_nxt (todrop) */
head_blk = tp->sackblks[0];
} else {
/* SACK block for the received segment. */
head_blk.start = rcv_start;
head_blk.end = rcv_end;
}
/*
* Merge updated SACK blocks into head_blk, and save unchanged SACK
* blocks into saved_blks[]. num_saved will have the number of the
* saved SACK blocks.
*/
num_saved = 0;
for (i = 0; i < tp->rcv_numsacks; i++) {
tcp_seq start = tp->sackblks[i].start;
tcp_seq end = tp->sackblks[i].end;
if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
/*
* Discard this SACK block.
*/
} else if (SEQ_LEQ(head_blk.start, end) &&
SEQ_GEQ(head_blk.end, start)) {
/*
* Merge this SACK block into head_blk. This SACK
* block itself will be discarded.
*/
/*
* |-|
* |---| merge
*
* |-|
* |---| merge
*
* |-----|
* |-| DSACK smaller
*
* |-|
* |-----| DSACK smaller
*/
if (head_blk.start == end)
head_blk.start = start;
else if (head_blk.end == start)
head_blk.end = end;
else {
if (SEQ_LT(head_blk.start, start)) {
tcp_seq temp = start;
start = head_blk.start;
head_blk.start = temp;
}
if (SEQ_GT(head_blk.end, end)) {
tcp_seq temp = end;
end = head_blk.end;
head_blk.end = temp;
}
if ((head_blk.start != start) ||
(head_blk.end != end)) {
if ((num_saved >= 1) &&
SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
SEQ_LEQ(saved_blks[num_saved-1].end, end))
num_saved--;
saved_blks[num_saved].start = start;
saved_blks[num_saved].end = end;
num_saved++;
}
}
} else {
/*
* This block supercedes the prior block
*/
if ((num_saved >= 1) &&
SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
SEQ_LEQ(saved_blks[num_saved-1].end, end))
num_saved--;
/*
* Save this SACK block.
*/
saved_blks[num_saved].start = start;
saved_blks[num_saved].end = end;
num_saved++;
}
}
/*
* Update SACK list in tp->sackblks[].
*/
num_head = 0;
if (SEQ_LT(rcv_start, rcv_end)) {
/*
* The received data segment is an out-of-order segment. Put
* head_blk at the top of SACK list.
*/
tp->sackblks[0] = head_blk;
num_head = 1;
/*
* If the number of saved SACK blocks exceeds its limit,
* discard the last SACK block.
*/
if (num_saved >= MAX_SACK_BLKS)
num_saved--;
}
if ((rcv_start == rcv_end) &&
(rcv_start == tp->sackblks[0].end)) {
num_head = 1;
}
if (num_saved > 0) {
/*
* Copy the saved SACK blocks back.
*/
bcopy(saved_blks, &tp->sackblks[num_head],
sizeof(struct sackblk) * num_saved);
}
/* Save the number of SACK blocks. */
tp->rcv_numsacks = num_head + num_saved;
}
void
tcp_clean_dsack_blocks(struct tcpcb *tp)
{
struct sackblk saved_blks[MAX_SACK_BLKS];
int num_saved, i;
INP_WLOCK_ASSERT(tp->t_inpcb);
/*
* Clean up any DSACK blocks that
* are in our queue of sack blocks.
*
*/
num_saved = 0;
for (i = 0; i < tp->rcv_numsacks; i++) {
tcp_seq start = tp->sackblks[i].start;
tcp_seq end = tp->sackblks[i].end;
if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
/*
* Discard this D-SACK block.
*/
continue;
}
/*
* Save this SACK block.
*/
saved_blks[num_saved].start = start;
saved_blks[num_saved].end = end;
num_saved++;
}
if (num_saved > 0) {
/*
* Copy the saved SACK blocks back.
*/
bcopy(saved_blks, &tp->sackblks[0],
sizeof(struct sackblk) * num_saved);
}
tp->rcv_numsacks = num_saved;
}
/*
* Delete all receiver-side SACK information.
*/
void
tcp_clean_sackreport(struct tcpcb *tp)
{
int i;
INP_WLOCK_ASSERT(tp->t_inpcb);
tp->rcv_numsacks = 0;
for (i = 0; i < MAX_SACK_BLKS; i++)
tp->sackblks[i].start = tp->sackblks[i].end=0;
}
/*
* Allocate struct sackhole.
*/
static struct sackhole *
tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
{
struct sackhole *hole;
if (tp->snd_numholes >= V_tcp_sack_maxholes ||
V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
TCPSTAT_INC(tcps_sack_sboverflow);
return NULL;
}
hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
if (hole == NULL)
return NULL;
hole->start = start;
hole->end = end;
hole->rxmit = start;
tp->snd_numholes++;
atomic_add_int(&V_tcp_sack_globalholes, 1);
return hole;
}
/*
* Free struct sackhole.
*/
static void
tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
{
uma_zfree(V_sack_hole_zone, hole);
tp->snd_numholes--;
atomic_subtract_int(&V_tcp_sack_globalholes, 1);
KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
}
/*
* Insert new SACK hole into scoreboard.
*/
static struct sackhole *
tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
struct sackhole *after)
{
struct sackhole *hole;
/* Allocate a new SACK hole. */
hole = tcp_sackhole_alloc(tp, start, end);
if (hole == NULL)
return NULL;
/* Insert the new SACK hole into scoreboard. */
if (after != NULL)
TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
else
TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
/* Update SACK hint. */
if (tp->sackhint.nexthole == NULL)
tp->sackhint.nexthole = hole;
return hole;
}
/*
* Remove SACK hole from scoreboard.
*/
static void
tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
{
/* Update SACK hint. */
if (tp->sackhint.nexthole == hole)
tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
/* Remove this SACK hole. */
TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
/* Free this SACK hole. */
tcp_sackhole_free(tp, hole);
}
/*
* Process cumulative ACK and the TCP SACK option to update the scoreboard.
* tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
* the sequence space).
* Returns 1 if incoming ACK has previously unknown SACK information,
* 0 otherwise.
*/
int
tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
{
struct sackhole *cur, *temp;
struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
int i, j, num_sack_blks, sack_changed;
int delivered_data, left_edge_delta;
INP_WLOCK_ASSERT(tp->t_inpcb);
num_sack_blks = 0;
sack_changed = 0;
delivered_data = 0;
left_edge_delta = 0;
/*
* If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
* treat [SND.UNA, SEG.ACK) as if it is a SACK block.
* Account changes to SND.UNA always in delivered data.
*/
if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
left_edge_delta = th_ack - tp->snd_una;
sack_blocks[num_sack_blks].start = tp->snd_una;
sack_blocks[num_sack_blks++].end = th_ack;
/*
* Pulling snd_fack forward if we got here
* due to DSACK blocks
*/
if (SEQ_LT(tp->snd_fack, th_ack)) {
delivered_data += th_ack - tp->snd_una;
tp->snd_fack = th_ack;
sack_changed = 1;
}
}
/*
* Append received valid SACK blocks to sack_blocks[], but only if we
* received new blocks from the other side.
*/
if (to->to_flags & TOF_SACK) {
for (i = 0; i < to->to_nsacks; i++) {
bcopy((to->to_sacks + i * TCPOLEN_SACK),
&sack, sizeof(sack));
sack.start = ntohl(sack.start);
sack.end = ntohl(sack.end);
if (SEQ_GT(sack.end, sack.start) &&
SEQ_GT(sack.start, tp->snd_una) &&
SEQ_GT(sack.start, th_ack) &&
SEQ_LT(sack.start, tp->snd_max) &&
SEQ_GT(sack.end, tp->snd_una) &&
SEQ_LEQ(sack.end, tp->snd_max)) {
sack_blocks[num_sack_blks++] = sack;
}
}
}
/*
* Return if SND.UNA is not advanced and no valid SACK block is
* received.
*/
if (num_sack_blks == 0)
return (sack_changed);
/*
* Sort the SACK blocks so we can update the scoreboard with just one
* pass. The overhead of sorting up to 4+1 elements is less than
* making up to 4+1 passes over the scoreboard.
*/
for (i = 0; i < num_sack_blks; i++) {
for (j = i + 1; j < num_sack_blks; j++) {
if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
sack = sack_blocks[i];
sack_blocks[i] = sack_blocks[j];
sack_blocks[j] = sack;
}
}
}
if (TAILQ_EMPTY(&tp->snd_holes)) {
/*
* Empty scoreboard. Need to initialize snd_fack (it may be
* uninitialized or have a bogus value). Scoreboard holes
* (from the sack blocks received) are created later below
* (in the logic that adds holes to the tail of the
* scoreboard).
*/
tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
tp->sackhint.sacked_bytes = 0; /* reset */
}
/*
* In the while-loop below, incoming SACK blocks (sack_blocks[]) and
* SACK holes (snd_holes) are traversed from their tails with just
* one pass in order to reduce the number of compares especially when
* the bandwidth-delay product is large.
*
* Note: Typically, in the first RTT of SACK recovery, the highest
* three or four SACK blocks with the same ack number are received.
* In the second RTT, if retransmitted data segments are not lost,
* the highest three or four SACK blocks with ack number advancing
* are received.
*/
sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */
tp->sackhint.last_sack_ack = sblkp->end;
if (SEQ_LT(tp->snd_fack, sblkp->start)) {
/*
* The highest SACK block is beyond fack. First,
* check if there was a successful Rescue Retransmission,
* and move this hole left. With normal holes, snd_fack
* is always to the right of the end.
*/
if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
SEQ_LEQ(tp->snd_fack,temp->end)) {
temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
temp->end = sblkp->start;
temp->rxmit = temp->start;
delivered_data += sblkp->end - sblkp->start;
tp->snd_fack = sblkp->end;
sblkp--;
sack_changed = 1;
} else {
/*
* Append a new SACK hole at the tail. If the
* second or later highest SACK blocks are also
* beyond the current fack, they will be inserted
* by way of hole splitting in the while-loop below.
*/
temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
if (temp != NULL) {
delivered_data += sblkp->end - sblkp->start;
tp->snd_fack = sblkp->end;
/* Go to the previous sack block. */
sblkp--;
sack_changed = 1;
} else {
/*
* We failed to add a new hole based on the current
* sack block. Skip over all the sack blocks that
* fall completely to the right of snd_fack and
* proceed to trim the scoreboard based on the
* remaining sack blocks. This also trims the
* scoreboard for th_ack (which is sack_blocks[0]).
*/
while (sblkp >= sack_blocks &&
SEQ_LT(tp->snd_fack, sblkp->start))
sblkp--;
if (sblkp >= sack_blocks &&
SEQ_LT(tp->snd_fack, sblkp->end)) {
delivered_data += sblkp->end - tp->snd_fack;
tp->snd_fack = sblkp->end;
sack_changed = 1;
}
}
}
} else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
/* fack is advanced. */
delivered_data += sblkp->end - tp->snd_fack;
tp->snd_fack = sblkp->end;
sack_changed = 1;
}
cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
/*
* Since the incoming sack blocks are sorted, we can process them
* making one sweep of the scoreboard.
*/
while (sblkp >= sack_blocks && cur != NULL) {
if (SEQ_GEQ(sblkp->start, cur->end)) {
/*
* SACKs data beyond the current hole. Go to the
* previous sack block.
*/
sblkp--;
continue;
}
if (SEQ_LEQ(sblkp->end, cur->start)) {
/*
* SACKs data before the current hole. Go to the
* previous hole.
*/
cur = TAILQ_PREV(cur, sackhole_head, scblink);
continue;
}
tp->sackhint.sack_bytes_rexmit -=
(SEQ_MIN(cur->rxmit, cur->end) - cur->start);
KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
("sackhint bytes rtx >= 0"));
sack_changed = 1;
if (SEQ_LEQ(sblkp->start, cur->start)) {
/* Data acks at least the beginning of hole. */
if (SEQ_GEQ(sblkp->end, cur->end)) {
/* Acks entire hole, so delete hole. */
delivered_data += (cur->end - cur->start);
temp = cur;
cur = TAILQ_PREV(cur, sackhole_head, scblink);
tcp_sackhole_remove(tp, temp);
/*
* The sack block may ack all or part of the
* next hole too, so continue onto the next
* hole.
*/
continue;
} else {
/* Move start of hole forward. */
delivered_data += (sblkp->end - cur->start);
cur->start = sblkp->end;
cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
}
} else {
/* Data acks at least the end of hole. */
if (SEQ_GEQ(sblkp->end, cur->end)) {
/* Move end of hole backward. */
delivered_data += (cur->end - sblkp->start);
cur->end = sblkp->start;
cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
cur->rxmit = tp->snd_recover;
} else {
/*
* ACKs some data in middle of a hole; need
* to split current hole
*/
temp = tcp_sackhole_insert(tp, sblkp->end,
cur->end, cur);
if (temp != NULL) {
if (SEQ_GT(cur->rxmit, temp->rxmit)) {
temp->rxmit = cur->rxmit;
tp->sackhint.sack_bytes_rexmit +=
(SEQ_MIN(temp->rxmit,
temp->end) - temp->start);
}
cur->end = sblkp->start;
cur->rxmit = SEQ_MIN(cur->rxmit,
cur->end);
if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
cur->rxmit = tp->snd_recover;
delivered_data += (sblkp->end - sblkp->start);
}
}
}
tp->sackhint.sack_bytes_rexmit +=
(SEQ_MIN(cur->rxmit, cur->end) - cur->start);
/*
* Testing sblkp->start against cur->start tells us whether
* we're done with the sack block or the sack hole.
* Accordingly, we advance one or the other.
*/
if (SEQ_LEQ(sblkp->start, cur->start))
cur = TAILQ_PREV(cur, sackhole_head, scblink);
else
sblkp--;
}
if (!(to->to_flags & TOF_SACK))
/*
* If this ACK did not contain any
* SACK blocks, any only moved the
* left edge right, it is a pure
* cumulative ACK. Do not count
* DupAck for this. Also required
* for RFC6675 rescue retransmission.
*/
sack_changed = 0;
tp->sackhint.delivered_data = delivered_data;
tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
KASSERT((delivered_data >= 0), ("delivered_data < 0"));
KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
return (sack_changed);
}
/*
* Free all SACK holes to clear the scoreboard.
*/
void
tcp_free_sackholes(struct tcpcb *tp)
{
struct sackhole *q;
INP_WLOCK_ASSERT(tp->t_inpcb);
while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
tcp_sackhole_remove(tp, q);
tp->sackhint.sack_bytes_rexmit = 0;
KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
KASSERT(tp->sackhint.nexthole == NULL,
("tp->sackhint.nexthole == NULL"));
}
/*
* Partial ack handling within a sack recovery episode. Keeping this very
* simple for now. When a partial ack is received, force snd_cwnd to a value
* that will allow the sender to transmit no more than 2 segments. If
* necessary, a better scheme can be adopted at a later point, but for now,
* the goal is to prevent the sender from bursting a large amount of data in
* the midst of sack recovery.
*/
void
tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
{
int num_segs = 1;
u_int maxseg = tcp_maxseg(tp);
INP_WLOCK_ASSERT(tp->t_inpcb);
tcp_timer_activate(tp, TT_REXMT, 0);
tp->t_rtttime = 0;
/* Send one or 2 segments based on how much new data was acked. */
if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
num_segs = 2;
tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
(tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
if (tp->snd_cwnd > tp->snd_ssthresh)
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_flags |= TF_ACKNOW;
/*
* RFC6675 rescue retransmission
* Add a hole between th_ack (snd_una is not yet set) and snd_max,
* if this was a pure cumulative ACK and no data was send beyond
* recovery point. Since the data in the socket has not been freed
* at this point, we check if the scoreboard is empty, and the ACK
* delivered some new data, indicating a full ACK. Also, if the
* recovery point is still at snd_max, we are probably application
* limited. However, this inference might not always be true. The
* rescue retransmission may rarely be slightly premature
* compared to RFC6675.
* The corresponding ACK+SACK will cause any further outstanding
* segments to be retransmitted. This addresses a corner case, when
* the trailing packets of a window are lost and no further data
* is available for sending.
*/
if ((V_tcp_do_newsack) &&
SEQ_LT(th->th_ack, tp->snd_recover) &&
(tp->snd_recover == tp->snd_max) &&
TAILQ_EMPTY(&tp->snd_holes) &&
(tp->sackhint.delivered_data > 0)) {
/*
* Exclude FIN sequence space in
* the hole for the rescue retransmission,
* and also don't create a hole, if only
* the ACK for a FIN is outstanding.
*/
tcp_seq highdata = tp->snd_max;
if (tp->t_flags & TF_SENTFIN)
highdata--;
if (th->th_ack != highdata) {
tp->snd_fack = th->th_ack;
(void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
highdata - maxseg), highdata, NULL);
}
}
(void) tp->t_fb->tfb_tcp_output(tp);
}
#if 0
/*
* Debug version of tcp_sack_output() that walks the scoreboard. Used for
* now to sanity check the hint.
*/
static struct sackhole *
tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
{
struct sackhole *p;
INP_WLOCK_ASSERT(tp->t_inpcb);
*sack_bytes_rexmt = 0;
TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
if (SEQ_LT(p->rxmit, p->end)) {
if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
continue;
}
*sack_bytes_rexmt += (p->rxmit - p->start);
break;
}
*sack_bytes_rexmt += (SEQ_MIN(p->rxmit, p->end) - p->start);
}
return (p);
}
#endif
/*
* Returns the next hole to retransmit and the number of retransmitted bytes
* from the scoreboard. We store both the next hole and the number of
* retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
* reception). This avoids scoreboard traversals completely.
*
* The loop here will traverse *at most* one link. Here's the argument. For
* the loop to traverse more than 1 link before finding the next hole to
* retransmit, we would need to have at least 1 node following the current
* hint with (rxmit == end). But, for all holes following the current hint,
* (start == rxmit), since we have not yet retransmitted from them.
* Therefore, in order to traverse more 1 link in the loop below, we need to
* have at least one node following the current hint with (start == rxmit ==
* end). But that can't happen, (start == end) means that all the data in
* that hole has been sacked, in which case, the hole would have been removed
* from the scoreboard.
*/
struct sackhole *
tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
{
struct sackhole *hole = NULL;
INP_WLOCK_ASSERT(tp->t_inpcb);
*sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
hole = tp->sackhint.nexthole;
if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
goto out;
while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
if (SEQ_LT(hole->rxmit, hole->end)) {
tp->sackhint.nexthole = hole;
break;
}
}
out:
return (hole);
}
/*
* After a timeout, the SACK list may be rebuilt. This SACK information
* should be used to avoid retransmitting SACKed data. This function
* traverses the SACK list to see if snd_nxt should be moved forward.
*/
void
tcp_sack_adjust(struct tcpcb *tp)
{
struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
INP_WLOCK_ASSERT(tp->t_inpcb);
if (cur == NULL)
return; /* No holes */
if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
return; /* We're already beyond any SACKed blocks */
/*-
* Two cases for which we want to advance snd_nxt:
* i) snd_nxt lies between end of one hole and beginning of another
* ii) snd_nxt lies between end of last hole and snd_fack
*/
while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
if (SEQ_LT(tp->snd_nxt, cur->end))
return;
if (SEQ_GEQ(tp->snd_nxt, p->start))
cur = p;
else {
tp->snd_nxt = p->start;
return;
}
}
if (SEQ_LT(tp->snd_nxt, cur->end))
return;
tp->snd_nxt = tp->snd_fack;
}
/*
* Lost Retransmission Detection
* Check is FACK is beyond the rexmit of the leftmost hole.
* If yes, we restart sending from still existing holes,
* and adjust cwnd via the congestion control module.
*/
void
tcp_sack_lost_retransmission(struct tcpcb *tp, struct tcphdr *th)
{
struct sackhole *temp;
uint32_t prev_cwnd;
if (IN_RECOVERY(tp->t_flags) &&
SEQ_GT(tp->snd_fack, tp->snd_recover) &&
((temp = TAILQ_FIRST(&tp->snd_holes)) != NULL) &&
SEQ_GEQ(temp->rxmit, temp->end) &&
SEQ_GEQ(tp->snd_fack, temp->rxmit)) {
TCPSTAT_INC(tcps_sack_lostrexmt);
/*
* Start retransmissions from the first hole, and
* subsequently all other remaining holes, including
* those, which had been sent completely before.
*/
tp->sackhint.nexthole = temp;
TAILQ_FOREACH(temp, &tp->snd_holes, scblink) {
if (SEQ_GEQ(tp->snd_fack, temp->rxmit) &&
SEQ_GEQ(temp->rxmit, temp->end))
temp->rxmit = temp->start;
}
/*
* Remember the old ssthresh, to deduct the beta factor used
* by the CC module. Finally, set cwnd to ssthresh just
* prior to invoking another cwnd reduction by the CC
* module, to not shrink it excessively.
*/
prev_cwnd = tp->snd_cwnd;
tp->snd_cwnd = tp->snd_ssthresh;
/*
* Formally exit recovery, and let the CC module adjust
* ssthresh as intended.
*/
EXIT_RECOVERY(tp->t_flags);
cc_cong_signal(tp, th, CC_NDUPACK);
/*
* For PRR, adjust recover_fs as if this new reduction
* initialized this variable.
* cwnd will be adjusted by SACK or PRR processing
* subsequently, only set it to a safe value here.
*/
tp->snd_cwnd = tcp_maxseg(tp);
tp->sackhint.recover_fs = (tp->snd_max - tp->snd_una) -
tp->sackhint.recover_fs;
}
}
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