This change represents a substantial restructure of the way we

reassembly inbound tcp segments. The old algorithm just blindly
dropped in segments without coalescing. This meant that every
segment could take up greater and greater room on the linked list
of segments. This of course is now subject to a tighter limit (100)
of segments which in a high BDP situation will cause us to be a
lot more in-efficent as we drop segments beyond 100 entries that
we receive. What this restructure does is cause the reassembly
buffer to coalesce segments putting an emphasis on the two
common cases (which avoid walking the list of segments) i.e.
where we add to the back of the queue of segments and where we
add to the front. We also have the reassembly buffer supporting
a couple of debug options (black box logging as well as counters
for code coverage). These are compiled out by default but can
be added by uncommenting the defines.

Sponsored by:	Netflix Inc.
Differential Revision:	https://reviews.freebsd.org/D16626

1 files changed, 11 insertions, 5 deletions

diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index 5f8c0ade6700..2fbe07ade5dc 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -46,12 +46,15 @@
 #if defined(_KERNEL) || defined(_WANT_TCPCB)
 /* TCP segment queue entry */
 struct tseg_qent {
-	LIST_ENTRY(tseg_qent) tqe_q;
+	TAILQ_ENTRY(tseg_qent) tqe_q;
+	struct	mbuf   *tqe_m;		/* mbuf contains packet */
+	struct  mbuf   *tqe_last;	/* last mbuf in chain */
+	tcp_seq tqe_start;		/* TCP Sequence number start */
 	int	tqe_len;		/* TCP segment data length */
-	struct	tcphdr *tqe_th;		/* a pointer to tcp header */
-	struct	mbuf	*tqe_m;		/* mbuf contains packet */
+	uint32_t tqe_flags;		/* The flags from the th->th_flags */
+	uint32_t tqe_mbuf_cnt;		/* Count of mbuf overhead */
 };
-LIST_HEAD(tsegqe_head, tseg_qent);
+TAILQ_HEAD(tsegqe_head, tseg_qent);
 
 struct sackblk {
 	tcp_seq start;		/* start seq no. of sack block */
@@ -79,6 +82,8 @@ struct sackhint {
 	uint64_t	_pad[1];	/* TBD */
 };
 
+#define SEGQ_EMPTY(tp) TAILQ_EMPTY(&(tp)->t_segq)
+
 STAILQ_HEAD(tcp_log_stailq, tcp_log_mem);
 
 /*
@@ -131,6 +136,7 @@ struct tcpcb {
 	/* Cache line 3 */
 	tcp_seq	rcv_up;			/* receive urgent pointer */
 	int	t_segqlen;		/* segment reassembly queue length */
+	uint32_t t_segqmbuflen;		/* Count of bytes mbufs on all entries */
 	struct	tsegqe_head t_segq;	/* segment reassembly queue */
 	struct mbuf      *t_in_pkt;
 	struct mbuf	 *t_tail_pkt;
@@ -837,7 +843,7 @@ char	*tcp_log_addrs(struct in_conninfo *, struct tcphdr *, void *,
 	    const void *);
 char	*tcp_log_vain(struct in_conninfo *, struct tcphdr *, void *,
 	    const void *);
-int	 tcp_reass(struct tcpcb *, struct tcphdr *, int *, struct mbuf *);
+int	 tcp_reass(struct tcpcb *, struct tcphdr *, tcp_seq *, int *, struct mbuf *);
 void	 tcp_reass_global_init(void);
 void	 tcp_reass_flush(struct tcpcb *);
 void	 tcp_dooptions(struct tcpopt *, u_char *, int, int);