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 <eduma...@google.com>
Cc: Neal Cardwell <ncardw...@google.com>
Cc: Yuchung Cheng <ych...@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
