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Date: Wed, 5 Dec 2007 13:18:14 +0200 (EET)
From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To: David Miller <davem@...emloft.net>
cc: Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/3] [TCP]: NAGLE_PUSH seems to be a wrong way around
On Wed, 5 Dec 2007, David Miller wrote:
> From: "Ilpo_Järvinen" <ilpo.jarvinen@...sinki.fi>
> Date: Tue, 4 Dec 2007 18:48:50 +0200
>
> > The comment in tcp_nagle_test suggests that. This bug is very
> > very old, even 2.4.0 seems to have it.
> >
> > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
>
> Wow, I can't believed I missed this during the TSO output
> path rewrite.
>
> I will have to double check the history, because I stated
> at these conditionals many times during that work and I
> wonder if I inverted a "!" somewhere along the line.
...No need, I mostly digged this up already because I was bit unsure
how it should be, your conversions didn't invert anything significant,
at least before 2.4.0 :-). ...Unless you first fixed it and then
broke it again (in your private working tree)... :-/
...If I understood the very old history correctly, this bug was introduced
in 2.4.0-test12 which inverted !tail incorrectly to nonagle==1.
You can check include/net/tcp.h diffs from this commit:
http://www.linux-mips.org/git?p=linux.git;a=commitdiff;h=c9c06167e7933d93a6e396174c68abf242294abb
...Though it's very large one. So I included only the relevant portion
here below.
--
i.
c9c06167e7933d93a6e396174c68abf242294abb
diff --git a/include/net/tcp.h b/include/net/tcp.h
index dd8e74c..ccdff5a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -328,9 +328,13 @@ static __inline__ int tcp_sk_listen_hashfn(struct sock *sk)
*/
#define TCP_DELACK_MAX (HZ/5) /* maximal time to delay before sending an ACK */
-#define TCP_DELACK_MIN (2) /* minimal time to delay before sending an ACK,
- * 2 scheduler ticks, not depending on HZ. */
-#define TCP_ATO_MIN 2
+#if HZ >= 100
+#define TCP_DELACK_MIN (HZ/25) /* minimal time to delay before sending an ACK */
+#define TCP_ATO_MIN (HZ/25)
+#else
+#define TCP_DELACK_MIN 4
+#define TCP_ATO_MIN 4
+#endif
#define TCP_RTO_MAX (120*HZ)
#define TCP_RTO_MIN (HZ/5)
#define TCP_TIMEOUT_INIT (3*HZ) /* RFC 1122 initial RTO value */
@@ -688,6 +692,10 @@ static __inline__ void tcp_delack_init(struct tcp_opt *tp)
memset(&tp->ack, 0, sizeof(tp->ack));
}
+static inline void tcp_clear_options(struct tcp_opt *tp)
+{
+ tp->tstamp_ok = tp->sack_ok = tp->wscale_ok = tp->snd_wscale = 0;
+}
enum tcp_tw_status
{
@@ -734,7 +742,8 @@ extern int tcp_recvmsg(struct sock *sk,
extern int tcp_listen_start(struct sock *sk);
extern void tcp_parse_options(struct sk_buff *skb,
- struct tcp_opt *tp);
+ struct tcp_opt *tp,
+ int estab);
/*
* TCP v4 functions exported for the inet6 API
@@ -997,6 +1006,9 @@ struct tcp_skb_cb {
#define TCPCB_EVER_RETRANS 0x80 /* Ever retransmitted frame */
#define TCPCB_RETRANS (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS)
+#define TCPCB_URG 0x20 /* Urgent pointer advenced here */
+
+#define TCPCB_AT_TAIL (TCPCB_URG)
__u16 urg_ptr; /* Valid w/URG flags is set. */
__u32 ack_seq; /* Sequence number ACK'd */
@@ -1134,18 +1146,19 @@ static __inline__ void tcp_minshall_update(struct tcp_opt *tp, int mss, struct s
/* Return 0, if packet can be sent now without violation Nagle's rules:
1. It is full sized.
- 2. Or it contains FIN or URG.
+ 2. Or it contains FIN.
3. Or TCP_NODELAY was set.
4. Or TCP_CORK is not set, and all sent packets are ACKed.
With Minshall's modification: all sent small packets are ACKed.
*/
-static __inline__ int tcp_nagle_check(struct tcp_opt *tp, struct sk_buff *skb, unsigned mss_now)
+static __inline__ int
+tcp_nagle_check(struct tcp_opt *tp, struct sk_buff *skb, unsigned mss_now, int nonagle)
{
return (skb->len < mss_now &&
- !(TCP_SKB_CB(skb)->flags & (TCPCB_FLAG_URG|TCPCB_FLAG_FIN)) &&
- (tp->nonagle == 2 ||
- (!tp->nonagle &&
+ !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
+ (nonagle == 2 ||
+ (!nonagle &&
tp->packets_out &&
tcp_minshall_check(tp))));
}
@@ -1154,7 +1167,7 @@ static __inline__ int tcp_nagle_check(struct tcp_opt *tp, struct sk_buff *skb, u
* should be put on the wire right now.
*/
static __inline__ int tcp_snd_test(struct tcp_opt *tp, struct sk_buff *skb,
- unsigned cur_mss, int tail)
+ unsigned cur_mss, int nonagle)
{
/* RFC 1122 - section 4.2.3.4
*
@@ -1180,8 +1193,8 @@ static __inline__ int tcp_snd_test(struct tcp_opt *tp, struct sk_buff *skb,
/* Don't be strict about the congestion window for the
* final FIN frame. -DaveM
*/
- return ((!tail || !tcp_nagle_check(tp, skb, cur_mss) ||
- skb_tailroom(skb) < 32) &&
+ return ((nonagle==1 || tp->urg_mode
+ || !tcp_nagle_check(tp, skb, cur_mss, nonagle)) &&
((tcp_packets_in_flight(tp) < tp->snd_cwnd) ||
(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)) &&
!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una + tp->snd_wnd));
@@ -1204,12 +1217,15 @@ static __inline__ int tcp_skb_is_last(struct sock *sk, struct sk_buff *skb)
*/
static __inline__ void __tcp_push_pending_frames(struct sock *sk,
struct tcp_opt *tp,
- unsigned cur_mss)
+ unsigned cur_mss,
+ int nonagle)
{
struct sk_buff *skb = tp->send_head;
if (skb) {
- if (!tcp_snd_test(tp, skb, cur_mss, tcp_skb_is_last(sk, skb)) ||
+ if (!tcp_skb_is_last(sk, skb))
+ nonagle = 1;
+ if (!tcp_snd_test(tp, skb, cur_mss, nonagle) ||
tcp_write_xmit(sk))
tcp_check_probe_timer(sk, tp);
}
@@ -1219,7 +1235,7 @@ static __inline__ void __tcp_push_pending_frames(struct sock *sk,
static __inline__ void tcp_push_pending_frames(struct sock *sk,
struct tcp_opt *tp)
{
- __tcp_push_pending_frames(sk, tp, tcp_current_mss(sk));
+ __tcp_push_pending_frames(sk, tp, tcp_current_mss(sk), tp->nonagle);
}
static __inline__ int tcp_may_send_now(struct sock *sk, struct tcp_opt *tp)
@@ -1227,7 +1243,8 @@ static __inline__ int tcp_may_send_now(struct sock *sk, struct tcp_opt *tp)
struct sk_buff *skb = tp->send_head;
return (skb &&
- tcp_snd_test(tp, skb, tcp_current_mss(sk), tcp_skb_is_last(sk, skb)));
+ tcp_snd_test(tp, skb, tcp_current_mss(sk),
+ tcp_skb_is_last(sk, skb) ? 1 : tp->nonagle));
}
static __inline__ void tcp_init_wl(struct tcp_opt *tp, u32 ack, u32 seq)
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