* [PATCH v3 net-next 2/4] tcp: take care of compressed acks in tcp_add_reno_sack()
2018-11-27 22:41 [PATCH v3 net-next 0/4] tcp: take a bit more care of backlog stress Eric Dumazet
2018-11-27 22:42 ` [PATCH v3 net-next 1/4] tcp: hint compiler about sack flows Eric Dumazet
@ 2018-11-27 22:42 ` Eric Dumazet
2018-11-28 16:41 ` Neal Cardwell
2018-11-27 22:42 ` [PATCH v3 net-next 3/4] tcp: make tcp_space() aware of socket backlog Eric Dumazet
` (2 subsequent siblings)
4 siblings, 1 reply; 9+ messages in thread
From: Eric Dumazet @ 2018-11-27 22:42 UTC (permalink / raw)
To: David S . Miller
Cc: netdev, Jean-Louis Dupond, Neal Cardwell, Yuchung Cheng,
Eric Dumazet, Eric Dumazet
Neal pointed out that non sack flows might suffer from ACK compression
added in the following patch ("tcp: implement coalescing on backlog queue")
Instead of tweaking tcp_add_backlog() we can take into
account how many ACK were coalesced, this information
will be available in skb_shinfo(skb)->gso_segs
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
net/ipv4/tcp_input.c | 58 +++++++++++++++++++++++++-------------------
1 file changed, 33 insertions(+), 25 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f32397890b6dcbc34976954c4be142108efa04d8..e5f3819ad859f6e6ca28e09c0f2dbdb7052708ee 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1863,16 +1863,20 @@ static void tcp_check_reno_reordering(struct sock *sk, const int addend)
/* Emulate SACKs for SACKless connection: account for a new dupack. */
-static void tcp_add_reno_sack(struct sock *sk)
+static void tcp_add_reno_sack(struct sock *sk, int num_dupack)
{
- struct tcp_sock *tp = tcp_sk(sk);
- u32 prior_sacked = tp->sacked_out;
+ if (num_dupack) {
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 prior_sacked = tp->sacked_out;
+ s32 delivered;
- tp->sacked_out++;
- tcp_check_reno_reordering(sk, 0);
- if (tp->sacked_out > prior_sacked)
- tp->delivered++; /* Some out-of-order packet is delivered */
- tcp_verify_left_out(tp);
+ tp->sacked_out += num_dupack;
+ tcp_check_reno_reordering(sk, 0);
+ delivered = tp->sacked_out - prior_sacked;
+ if (delivered > 0)
+ tp->delivered += delivered;
+ tcp_verify_left_out(tp);
+ }
}
/* Account for ACK, ACKing some data in Reno Recovery phase. */
@@ -2634,7 +2638,7 @@ void tcp_enter_recovery(struct sock *sk, bool ece_ack)
/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
* recovered or spurious. Otherwise retransmits more on partial ACKs.
*/
-static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
+static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
int *rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
@@ -2653,7 +2657,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
return;
if (after(tp->snd_nxt, tp->high_seq)) {
- if (flag & FLAG_DATA_SACKED || is_dupack)
+ if (flag & FLAG_DATA_SACKED || num_dupack)
tp->frto = 0; /* Step 3.a. loss was real */
} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
tp->high_seq = tp->snd_nxt;
@@ -2679,8 +2683,8 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
/* A Reno DUPACK means new data in F-RTO step 2.b above are
* delivered. Lower inflight to clock out (re)tranmissions.
*/
- if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
- tcp_add_reno_sack(sk);
+ if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
+ tcp_add_reno_sack(sk, num_dupack);
else if (flag & FLAG_SND_UNA_ADVANCED)
tcp_reset_reno_sack(tp);
}
@@ -2757,13 +2761,13 @@ static bool tcp_force_fast_retransmit(struct sock *sk)
* tcp_xmit_retransmit_queue().
*/
static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
- bool is_dupack, int *ack_flag, int *rexmit)
+ int num_dupack, int *ack_flag, int *rexmit)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int fast_rexmit = 0, flag = *ack_flag;
- bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
- tcp_force_fast_retransmit(sk));
+ bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
+ tcp_force_fast_retransmit(sk));
if (!tp->packets_out && tp->sacked_out)
tp->sacked_out = 0;
@@ -2810,8 +2814,8 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
switch (icsk->icsk_ca_state) {
case TCP_CA_Recovery:
if (!(flag & FLAG_SND_UNA_ADVANCED)) {
- if (tcp_is_reno(tp) && is_dupack)
- tcp_add_reno_sack(sk);
+ if (tcp_is_reno(tp))
+ tcp_add_reno_sack(sk, num_dupack);
} else {
if (tcp_try_undo_partial(sk, prior_snd_una))
return;
@@ -2826,7 +2830,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
tcp_identify_packet_loss(sk, ack_flag);
break;
case TCP_CA_Loss:
- tcp_process_loss(sk, flag, is_dupack, rexmit);
+ tcp_process_loss(sk, flag, num_dupack, rexmit);
tcp_identify_packet_loss(sk, ack_flag);
if (!(icsk->icsk_ca_state == TCP_CA_Open ||
(*ack_flag & FLAG_LOST_RETRANS)))
@@ -2837,8 +2841,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
if (tcp_is_reno(tp)) {
if (flag & FLAG_SND_UNA_ADVANCED)
tcp_reset_reno_sack(tp);
- if (is_dupack)
- tcp_add_reno_sack(sk);
+ tcp_add_reno_sack(sk, num_dupack);
}
if (icsk->icsk_ca_state <= TCP_CA_Disorder)
@@ -3558,7 +3561,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
bool is_sack_reneg = tp->is_sack_reneg;
u32 ack_seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
- bool is_dupack = false;
+ int num_dupack = 0;
int prior_packets = tp->packets_out;
u32 delivered = tp->delivered;
u32 lost = tp->lost;
@@ -3669,8 +3672,13 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
tcp_set_xmit_timer(sk);
if (tcp_ack_is_dubious(sk, flag)) {
- is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
- tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+ if (!(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP))) {
+ num_dupack = 1;
+ /* Consider if pure acks were aggregated in tcp_add_backlog() */
+ if (!(flag & FLAG_DATA))
+ num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+ }
+ tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
&rexmit);
}
@@ -3688,7 +3696,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
no_queue:
/* If data was DSACKed, see if we can undo a cwnd reduction. */
if (flag & FLAG_DSACKING_ACK) {
- tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+ tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
&rexmit);
tcp_newly_delivered(sk, delivered, flag);
}
@@ -3713,7 +3721,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
if (TCP_SKB_CB(skb)->sacked) {
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
&sack_state);
- tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+ tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
&rexmit);
tcp_newly_delivered(sk, delivered, flag);
tcp_xmit_recovery(sk, rexmit);
--
2.20.0.rc0.387.gc7a69e6b6c-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH v3 net-next 4/4] tcp: implement coalescing on backlog queue
2018-11-27 22:41 [PATCH v3 net-next 0/4] tcp: take a bit more care of backlog stress Eric Dumazet
` (2 preceding siblings ...)
2018-11-27 22:42 ` [PATCH v3 net-next 3/4] tcp: make tcp_space() aware of socket backlog Eric Dumazet
@ 2018-11-27 22:42 ` Eric Dumazet
2018-11-28 16:46 ` Neal Cardwell
2018-11-30 21:27 ` [PATCH v3 net-next 0/4] tcp: take a bit more care of backlog stress David Miller
4 siblings, 1 reply; 9+ messages in thread
From: Eric Dumazet @ 2018-11-27 22:42 UTC (permalink / raw)
To: David S . Miller
Cc: netdev, Jean-Louis Dupond, Neal Cardwell, Yuchung Cheng,
Eric Dumazet, Eric Dumazet
In case GRO is not as efficient as it should be or disabled,
we might have a user thread trapped in __release_sock() while
softirq handler flood packets up to the point we have to drop.
This patch balances work done from user thread and softirq,
to give more chances to __release_sock() to complete its work
before new packets are added the the backlog.
This also helps if we receive many ACK packets, since GRO
does not aggregate them.
This patch brings ~60% throughput increase on a receiver
without GRO, but the spectacular gain is really on
1000x release_sock() latency reduction I have measured.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
---
include/uapi/linux/snmp.h | 1 +
net/ipv4/proc.c | 1 +
net/ipv4/tcp_ipv4.c | 92 ++++++++++++++++++++++++++++++++++++---
3 files changed, 88 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index f80135e5feaa886000009db6dff75b2bc2d637b2..86dc24a96c90ab047d5173d625450facd6c6dd79 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -243,6 +243,7 @@ enum
LINUX_MIB_TCPREQQFULLDROP, /* TCPReqQFullDrop */
LINUX_MIB_TCPRETRANSFAIL, /* TCPRetransFail */
LINUX_MIB_TCPRCVCOALESCE, /* TCPRcvCoalesce */
+ LINUX_MIB_TCPBACKLOGCOALESCE, /* TCPBacklogCoalesce */
LINUX_MIB_TCPOFOQUEUE, /* TCPOFOQueue */
LINUX_MIB_TCPOFODROP, /* TCPOFODrop */
LINUX_MIB_TCPOFOMERGE, /* TCPOFOMerge */
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 70289682a6701438aed99a00a9705c39fa4394d3..c3610b37bb4ce665b1976d8cc907b6dd0de42ab9 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -219,6 +219,7 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPRenoRecoveryFail", LINUX_MIB_TCPRENORECOVERYFAIL),
SNMP_MIB_ITEM("TCPSackRecoveryFail", LINUX_MIB_TCPSACKRECOVERYFAIL),
SNMP_MIB_ITEM("TCPRcvCollapsed", LINUX_MIB_TCPRCVCOLLAPSED),
+ SNMP_MIB_ITEM("TCPBacklogCoalesce", LINUX_MIB_TCPBACKLOGCOALESCE),
SNMP_MIB_ITEM("TCPDSACKOldSent", LINUX_MIB_TCPDSACKOLDSENT),
SNMP_MIB_ITEM("TCPDSACKOfoSent", LINUX_MIB_TCPDSACKOFOSENT),
SNMP_MIB_ITEM("TCPDSACKRecv", LINUX_MIB_TCPDSACKRECV),
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 795605a2327504b8a025405826e7e0ca8dc8501d..4904250a9aac5001410f9454258cbb8978bb8202 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1619,12 +1619,14 @@ int tcp_v4_early_demux(struct sk_buff *skb)
bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
{
u32 limit = sk->sk_rcvbuf + sk->sk_sndbuf;
-
- /* Only socket owner can try to collapse/prune rx queues
- * to reduce memory overhead, so add a little headroom here.
- * Few sockets backlog are possibly concurrently non empty.
- */
- limit += 64*1024;
+ struct skb_shared_info *shinfo;
+ const struct tcphdr *th;
+ struct tcphdr *thtail;
+ struct sk_buff *tail;
+ unsigned int hdrlen;
+ bool fragstolen;
+ u32 gso_segs;
+ int delta;
/* In case all data was pulled from skb frags (in __pskb_pull_tail()),
* we can fix skb->truesize to its real value to avoid future drops.
@@ -1636,6 +1638,84 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
skb_dst_drop(skb);
+ if (unlikely(tcp_checksum_complete(skb))) {
+ bh_unlock_sock(sk);
+ __TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
+ __TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+ return true;
+ }
+
+ /* Attempt coalescing to last skb in backlog, even if we are
+ * above the limits.
+ * This is okay because skb capacity is limited to MAX_SKB_FRAGS.
+ */
+ th = (const struct tcphdr *)skb->data;
+ hdrlen = th->doff * 4;
+ shinfo = skb_shinfo(skb);
+
+ if (!shinfo->gso_size)
+ shinfo->gso_size = skb->len - hdrlen;
+
+ if (!shinfo->gso_segs)
+ shinfo->gso_segs = 1;
+
+ tail = sk->sk_backlog.tail;
+ if (!tail)
+ goto no_coalesce;
+ thtail = (struct tcphdr *)tail->data;
+
+ if (TCP_SKB_CB(tail)->end_seq != TCP_SKB_CB(skb)->seq ||
+ TCP_SKB_CB(tail)->ip_dsfield != TCP_SKB_CB(skb)->ip_dsfield ||
+ ((TCP_SKB_CB(tail)->tcp_flags |
+ TCP_SKB_CB(skb)->tcp_flags) & TCPHDR_URG) ||
+ ((TCP_SKB_CB(tail)->tcp_flags ^
+ TCP_SKB_CB(skb)->tcp_flags) & (TCPHDR_ECE | TCPHDR_CWR)) ||
+#ifdef CONFIG_TLS_DEVICE
+ tail->decrypted != skb->decrypted ||
+#endif
+ thtail->doff != th->doff ||
+ memcmp(thtail + 1, th + 1, hdrlen - sizeof(*th)))
+ goto no_coalesce;
+
+ __skb_pull(skb, hdrlen);
+ if (skb_try_coalesce(tail, skb, &fragstolen, &delta)) {
+ thtail->window = th->window;
+
+ TCP_SKB_CB(tail)->end_seq = TCP_SKB_CB(skb)->end_seq;
+
+ if (after(TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(tail)->ack_seq))
+ TCP_SKB_CB(tail)->ack_seq = TCP_SKB_CB(skb)->ack_seq;
+
+ TCP_SKB_CB(tail)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
+
+ if (TCP_SKB_CB(skb)->has_rxtstamp) {
+ TCP_SKB_CB(tail)->has_rxtstamp = true;
+ tail->tstamp = skb->tstamp;
+ skb_hwtstamps(tail)->hwtstamp = skb_hwtstamps(skb)->hwtstamp;
+ }
+
+ /* Not as strict as GRO. We only need to carry mss max value */
+ skb_shinfo(tail)->gso_size = max(shinfo->gso_size,
+ skb_shinfo(tail)->gso_size);
+
+ gso_segs = skb_shinfo(tail)->gso_segs + shinfo->gso_segs;
+ skb_shinfo(tail)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
+
+ sk->sk_backlog.len += delta;
+ __NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPBACKLOGCOALESCE);
+ kfree_skb_partial(skb, fragstolen);
+ return false;
+ }
+ __skb_push(skb, hdrlen);
+
+no_coalesce:
+ /* Only socket owner can try to collapse/prune rx queues
+ * to reduce memory overhead, so add a little headroom here.
+ * Few sockets backlog are possibly concurrently non empty.
+ */
+ limit += 64*1024;
+
if (unlikely(sk_add_backlog(sk, skb, limit))) {
bh_unlock_sock(sk);
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPBACKLOGDROP);
--
2.20.0.rc0.387.gc7a69e6b6c-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread