tcp: implement coalescing on backlog queue

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>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2018-11-27 14:42:03 -08:00 committed by David S. Miller
parent 85bdf7db5b
commit 4f693b55c3
3 changed files with 88 additions and 6 deletions

View file

@ -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 */

View file

@ -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),

View file

@ -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);