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This adds in an optimization so that we only walk one

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time through the mbuf chain during copy and TSO limiting.
It is used by both Rack and now the FreeBSD stack.
Sponsored by:	Netflix Inc
Differential Revision: https://reviews.freebsd.org/D15937
This commit is contained in:
Randall Stewart 2018-06-21 21:03:58 +00:00
parent e93fdbe212
commit 581a046a8b
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=335502
1 changed files with 22 additions and 66 deletions
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88
sys/netinet/tcp_output.c
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@ -209,6 +209,8 @@ tcp_output(struct tcpcb *tp)
int32_t len;
uint32_t recwin, sendwin;
int off, flags, error = 0; /* Keep compiler happy */
u_int if_hw_tsomaxsegcount = 0;
u_int if_hw_tsomaxsegsize;
struct mbuf *m;
struct ip *ip = NULL;
#ifdef TCPDEBUG
@ -879,9 +881,6 @@ tcp_output(struct tcpcb *tp)
if (tso) {
u_int if_hw_tsomax;
u_int if_hw_tsomaxsegcount;
u_int if_hw_tsomaxsegsize;
struct mbuf *mb;
u_int moff;
int max_len;
@ -913,65 +912,6 @@ tcp_output(struct tcpcb *tp)
len = max_len;
}
}
/*
* Check if we should limit by maximum segment
* size and count:
*/
if (if_hw_tsomaxsegcount != 0 &&
if_hw_tsomaxsegsize != 0) {
/*
* Subtract one segment for the LINK
* and TCP/IP headers mbuf that will
* be prepended to this mbuf chain
* after the code in this section
* limits the number of mbufs in the
* chain to if_hw_tsomaxsegcount.
*/
if_hw_tsomaxsegcount -= 1;
max_len = 0;
mb = sbsndmbuf(&so->so_snd, off, &moff);
while (mb != NULL && max_len < len) {
u_int mlen;
u_int frags;
/*
* Get length of mbuf fragment
* and how many hardware frags,
* rounded up, it would use:
*/
mlen = (mb->m_len - moff);
frags = howmany(mlen,
if_hw_tsomaxsegsize);
/* Handle special case: Zero Length Mbuf */
if (frags == 0)
frags = 1;
/*
* Check if the fragment limit
* will be reached or exceeded:
*/
if (frags >= if_hw_tsomaxsegcount) {
max_len += min(mlen,
if_hw_tsomaxsegcount *
if_hw_tsomaxsegsize);
break;
}
max_len += mlen;
if_hw_tsomaxsegcount -= frags;
moff = 0;
mb = mb->m_next;
}
if (max_len <= 0) {
len = 0;
} else if (len > max_len) {
sendalot = 1;
len = max_len;
}
}
/*
* Prevent the last segment from being
* fractional unless the send sockbuf can be
@ -1006,7 +946,6 @@ tcp_output(struct tcpcb *tp)
*/
if (tp->t_flags & TF_NEEDFIN)
sendalot = 1;
} else {
len = tp->t_maxseg - optlen - ipoptlen;
sendalot = 1;
@ -1041,6 +980,7 @@ tcp_output(struct tcpcb *tp)
*/
if (len) {
struct mbuf *mb;
struct sockbuf *msb;
u_int moff;
if ((tp->t_flags & TF_FORCEDATA) && len == 1)
@ -1074,14 +1014,30 @@ tcp_output(struct tcpcb *tp)
* Start the m_copy functions from the closest mbuf
* to the offset in the socket buffer chain.
*/
mb = sbsndptr(&so->so_snd, off, len, &moff);
mb = sbsndptr_noadv(&so->so_snd, off, &moff);
if (len <= MHLEN - hdrlen - max_linkhdr) {
m_copydata(mb, moff, len,
mtod(m, caddr_t) + hdrlen);
if (SEQ_LT(tp->snd_nxt, tp->snd_max))
sbsndptr_adv(&so->so_snd, mb, len);
m->m_len += len;
} else {
m->m_next = m_copym(mb, moff, len, M_NOWAIT);
if (SEQ_LT(tp->snd_nxt, tp->snd_max))
msb = NULL;
else
msb = &so->so_snd;
m->m_next = tcp_m_copym(mb, moff,
&len, if_hw_tsomaxsegcount,
if_hw_tsomaxsegsize, msb);
if (len <= (tp->t_maxseg - optlen)) {
/*
* Must have ran out of mbufs for the copy
* shorten it to no longer need tso. Lets
* not put on sendalot since we are low on
* mbufs.
*/
tso = 0;
}
if (m->m_next == NULL) {
SOCKBUF_UNLOCK(&so->so_snd);
(void) m_free(m);