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tcp: remove prequeue support

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prequeue is a tcp receive optimization that moves part of rx processing
from bh to process context.

This only works if the socket being processed belongs to a process that
is blocked in recv on that socket.

In practice, this doesn't happen anymore that often because nowadays
servers tend to use an event driven (epoll) model.

Even normal client applications (web browsers) commonly use many tcp
connections in parallel.

This has measureable impact only in netperf (which uses plain recv and
thus allows prequeue use) from host to locally running vm (~4%), however,
there were no changes when using netperf between two physical hosts with
ixgbe interfaces.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal
2017-07-30 03:57:18 +02:00
committed by David S. Miller
parent 764646b08d
commit e7942d0633
8 changed files with 2 additions and 262 deletions
Download Patch File Download Diff File Expand all files Collapse all files

62
net/ipv4/tcp_input.c
View File

@@ -4611,22 +4611,6 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
goto out_of_window;
/* Ok. In sequence. In window. */
if (tp->ucopy.task == current &&
tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
sock_owned_by_user(sk) && !tp->urg_data) {
int chunk = min_t(unsigned int, skb->len,
tp->ucopy.len);
__set_current_state(TASK_RUNNING);
if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
tp->ucopy.len -= chunk;
tp->copied_seq += chunk;
eaten = (chunk == skb->len);
tcp_rcv_space_adjust(sk);
}
}
if (eaten <= 0) {
queue_and_out:
if (eaten < 0) {
@@ -5186,26 +5170,6 @@ static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *t
}
}
static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
{
struct tcp_sock *tp = tcp_sk(sk);
int chunk = skb->len - hlen;
int err;
if (skb_csum_unnecessary(skb))
err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
else
err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);
if (!err) {
tp->ucopy.len -= chunk;
tp->copied_seq += chunk;
tcp_rcv_space_adjust(sk);
}
return err;
}
/* Accept RST for rcv_nxt - 1 after a FIN.
* When tcp connections are abruptly terminated from Mac OSX (via ^C), a
* FIN is sent followed by a RST packet. The RST is sent with the same
@@ -5446,32 +5410,6 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
int eaten = 0;
bool fragstolen = false;
if (tp->ucopy.task == current &&
tp->copied_seq == tp->rcv_nxt &&
len - tcp_header_len <= tp->ucopy.len &&
sock_owned_by_user(sk)) {
__set_current_state(TASK_RUNNING);
if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
*/
if (tcp_header_len ==
(sizeof(struct tcphdr) +
TCPOLEN_TSTAMP_ALIGNED) &&
tp->rcv_nxt == tp->rcv_wup)
tcp_store_ts_recent(tp);
tcp_rcv_rtt_measure_ts(sk, skb);
__skb_pull(skb, tcp_header_len);
tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPHPHITSTOUSER);
eaten = 1;
}
}
if (!eaten) {
if (tcp_checksum_complete(skb))
goto csum_error;