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Optimize passing contiguous nocopy buffers to tcp_write

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While TCP_OVERSIZE works only when tcp_write() is used with
TCP_WRITE_FLAG_COPY, this new code achieves
similar benefits for the use case that the caller manages their own
send buffers and passes successive chunks of those to tcp_write()
without TCP_WRITE_FLAG_COPY.

In particular, if a buffer is passed to
tcp_write() that is adjacent in memory to the previously passed
buffer, it will be combined into the previous ROM pbuf reference
whenever possible, thus extending that ROM pbuf rather than allocating
a new ROM pbuf.

For the aforementioned use case, the advantages of this code are
twofold:
1) fewer ROM pbufs need to be allocated to send the same data, and,
2) the MAC layer gets outgoing TCP packets with shorter pbuf chains.

Original patch by Ambroz Bizjak <ambrop7@gmail.com>
Edited by David van Moolenbroek <david@minix3.org>
Signed-off-by: goldsimon <goldsimon@gmx.de>
This commit is contained in:
Ambroz Bizjak 2016-11-24 11:27:34 +01:00 committed by goldsimon
parent 4c8620e03b
commit 8ba7363d11
2 changed files with 49 additions and 18 deletions
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3
CHANGELOG
View File

@ -6,6 +6,9 @@ HISTORY
++ New features:
2016-11-24: Ambroz Bizjak, David van Moolenbroek
* tcp_out.c: Optimize passing contiguous nocopy buffers to tcp_write (bug #46290)
2016-11-16: Dirk Ziegelmeier
* sockets.c: added support for IPv6 mapped IPv4 addresses

38
src/core/tcp_out.c
View File

@ -377,6 +377,7 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
u16_t oversize = 0;
u16_t oversize_used = 0;
#endif /* TCP_OVERSIZE */
u16_t extendlen = 0;
#if TCP_CHECKSUM_ON_COPY
u16_t concat_chksum = 0;
u8_t concat_chksum_swapped = 0;
@ -480,6 +481,10 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
/*
* Phase 2: Chain a new pbuf to the end of pcb->unsent.
*
* As an exception when NOT copying the data, if the given data buffer
* directly follows the last unsent data buffer in memory, extend the last
* ROM pbuf reference to the buffer, thus saving a ROM pbuf allocation.
*
* We don't extend segments containing SYN/FIN flags or options
* (len==0). The new pbuf is kept in concat_p and pbuf_cat'ed at
* the end.
@ -506,25 +511,34 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
#if TCP_CHECKSUM_ON_COPY
concat_chksummed += seglen;
#endif /* TCP_CHECKSUM_ON_COPY */
queuelen += pbuf_clen(concat_p);
} else {
/* Data is not copied */
/* If the last unsent pbuf is of type PBUF_ROM, try to extend it. */
struct pbuf *p;
for (p = last_unsent->p; p->next != NULL; p = p->next);
if (p->type == PBUF_ROM && (const u8_t *)p->payload + p->len == (const u8_t *)arg) {
LWIP_ASSERT("tcp_write: ROM pbufs cannot be oversized", pos == 0);
extendlen = seglen;
} else {
if ((concat_p = pbuf_alloc(PBUF_RAW, seglen, PBUF_ROM)) == NULL) {
LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
("tcp_write: could not allocate memory for zero-copy pbuf\n"));
goto memerr;
}
/* reference the non-volatile payload data */
((struct pbuf_rom*)concat_p)->payload = (const u8_t*)arg + pos;
queuelen += pbuf_clen(concat_p);
}
#if TCP_CHECKSUM_ON_COPY
/* calculate the checksum of nocopy-data */
tcp_seg_add_chksum(~inet_chksum((const u8_t*)arg + pos, seglen), seglen,
&concat_chksum, &concat_chksum_swapped);
concat_chksummed += seglen;
#endif /* TCP_CHECKSUM_ON_COPY */
/* reference the non-volatile payload data */
((struct pbuf_rom*)concat_p)->payload = (const u8_t*)arg + pos;
}
pos += seglen;
queuelen += pbuf_clen(concat_p);
}
} else {
#if TCP_OVERSIZE
@ -669,15 +683,30 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
#endif /* TCP_OVERSIZE */
/*
* Phase 2: concat_p can be concatenated onto last_unsent->p
* Phase 2: concat_p can be concatenated onto last_unsent->p, unless we
* determined that the last ROM pbuf can be extended to include the new data.
*/
if (concat_p != NULL) {
LWIP_ASSERT("tcp_write: cannot concatenate when pcb->unsent is empty",
(last_unsent != NULL));
pbuf_cat(last_unsent->p, concat_p);
last_unsent->len += concat_p->tot_len;
} else if (extendlen > 0) {
struct pbuf *p;
LWIP_ASSERT("tcp_write: extension of reference requires reference",
last_unsent != NULL && last_unsent->p != NULL);
for (p = last_unsent->p; p->next != NULL; p = p->next) {
p->tot_len += extendlen;
}
p->tot_len += extendlen;
p->len += extendlen;
last_unsent->len += extendlen;
}
#if TCP_CHECKSUM_ON_COPY
if (concat_chksummed) {
LWIP_ASSERT("tcp_write: concat checksum needs concatenated data",
concat_p != NULL || extendlen > 0);
/*if concat checksumm swapped - swap it back */
if (concat_chksum_swapped) {
concat_chksum = SWAP_BYTES_IN_WORD(concat_chksum);
@ -687,7 +716,6 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
last_unsent->flags |= TF_SEG_DATA_CHECKSUMMED;
}
#endif /* TCP_CHECKSUM_ON_COPY */
}
/*
* Phase 3: Append queue to pcb->unsent. Queue may be NULL, but that