tcp_send_buffered.c: improve tcp write buffering
* Send data chunk-by-chunk
Note: A stream socket doesn't have atomicity requirement.
* Increase the chance to use full-sized segments
Benchmark numbers in my environment:
* Over ESP32 wifi
* The peer is NetBSD, which has traditional delayed ack TCP
* iperf uses 16384 bytes buffer
---
without this patch,
CONFIG_IOB_NBUFFERS=36
CONFIG_IOB_BUFSIZE=196
does not work.
see https://github.com/apache/incubator-nuttx/pull/2772#discussion_r592820639
---
without this patch,
CONFIG_IOB_NBUFFERS=128
CONFIG_IOB_BUFSIZE=196
```
nsh> iperf -c 192.168.8.1
IP: 192.168.8.103
mode=tcp-client sip=192.168.8.103:5001,dip=192.168.8.1:5001, interval=3, time=30
Interval Bandwidth
0- 3 sec, 4.11 Mbits/sec
3- 6 sec, 4.63 Mbits/sec
6- 9 sec, 4.89 Mbits/sec
9- 12 sec, 4.63 Mbits/sec
12- 15 sec, 4.85 Mbits/sec
15- 18 sec, 4.85 Mbits/sec
18- 21 sec, 5.02 Mbits/sec
21- 24 sec, 3.67 Mbits/sec
24- 27 sec, 4.94 Mbits/sec
27- 30 sec, 4.81 Mbits/sec
0- 30 sec, 4.64 Mbits/sec
nsh>
```
---
with this patch,
CONFIG_IOB_NBUFFERS=36
CONFIG_IOB_BUFSIZE=196
```
nsh> iperf -c 192.168.8.1
IP: 192.168.8.103
mode=tcp-client sip=192.168.8.103:5001,dip=192.168.8.1:5001, interval=3, time=30
Interval Bandwidth
0- 3 sec, 5.33 Mbits/sec
3- 6 sec, 5.59 Mbits/sec
6- 9 sec, 5.55 Mbits/sec
9- 12 sec, 5.59 Mbits/sec
12- 15 sec, 5.59 Mbits/sec
15- 18 sec, 5.72 Mbits/sec
18- 21 sec, 5.68 Mbits/sec
21- 24 sec, 5.29 Mbits/sec
24- 27 sec, 4.67 Mbits/sec
27- 30 sec, 4.50 Mbits/sec
0- 30 sec, 5.35 Mbits/sec
nsh>
```
---
with this patch,
CONFIG_IOB_NBUFFERS=128
CONFIG_IOB_BUFSIZE=196
```
nsh> iperf -c 192.168.8.1
IP: 192.168.8.103
mode=tcp-client sip=192.168.8.103:5001,dip=192.168.8.1:5001, interval=3, time=30
Interval Bandwidth
0- 3 sec, 5.51 Mbits/sec
3- 6 sec, 4.67 Mbits/sec
6- 9 sec, 4.54 Mbits/sec
9- 12 sec, 5.42 Mbits/sec
12- 15 sec, 5.37 Mbits/sec
15- 18 sec, 5.11 Mbits/sec
18- 21 sec, 5.07 Mbits/sec
21- 24 sec, 5.29 Mbits/sec
24- 27 sec, 5.77 Mbits/sec
27- 30 sec, 4.63 Mbits/sec
0- 30 sec, 5.14 Mbits/sec
nsh>
```
837e1a72a4