IBM REDP-4285-00 Manual De Usuario
Chapter 4. Tuning the operating system
129
Draft Document for Review May 4, 2007 11:35 am
4285ch04.fm
22:01:25.515601 IP plnxsu4.34088 > plnxsu5.40500: . 136734377:136735837(1460) ack 66752 win 46
22:01:25.515610 IP plnxsu4.34088 > plnxsu5.40500: . 136746057:136747517(1460) ack 66752 win 46
22:01:25.515617 IP plnxsu4.34088 > plnxsu5.40500: . 136757737:136759197(1460) ack 66752 win 46
22:01:25.515707 IP plnxsu5.40500 > plnxsu4.34088: . ack 136678897 win 3061
22:01:25.515714 IP plnxsu5.40500 > plnxsu4.34088: . ack 136681817 win 3061
22:01:25.515764 IP plnxsu5.40500 > plnxsu4.34088: . ack 136684737 win 3061
22:01:25.515768 IP plnxsu5.40500 > plnxsu4.34088: . ack 136687657 win 3061
22:01:25.515774 IP plnxsu5.40500 > plnxsu4.34088: . ack 136690577 win 3061
22:01:25.515610 IP plnxsu4.34088 > plnxsu5.40500: . 136746057:136747517(1460) ack 66752 win 46
22:01:25.515617 IP plnxsu4.34088 > plnxsu5.40500: . 136757737:136759197(1460) ack 66752 win 46
22:01:25.515707 IP plnxsu5.40500 > plnxsu4.34088: . ack 136678897 win 3061
22:01:25.515714 IP plnxsu5.40500 > plnxsu4.34088: . ack 136681817 win 3061
22:01:25.515764 IP plnxsu5.40500 > plnxsu4.34088: . ack 136684737 win 3061
22:01:25.515768 IP plnxsu5.40500 > plnxsu4.34088: . ack 136687657 win 3061
22:01:25.515774 IP plnxsu5.40500 > plnxsu4.34088: . ack 136690577 win 3061
Impact of socket buffer size
Small socket buffers may cause performance degradation when a server deals with many
concurrent large file transfer. As Figure 4-16 shows, a clear performance decline is observed
when using small socket buffers. A low value of rmem_max and wmem_max limit available socket
buffer sizes even if the peer has affordable socket buffers available. This causes small window
sizes and creates a performance ceiling for large data transfers. Though not included in this
chart, no clear performance difference is observed for small data (less than 4Kbytes) transfer.
concurrent large file transfer. As Figure 4-16 shows, a clear performance decline is observed
when using small socket buffers. A low value of rmem_max and wmem_max limit available socket
buffer sizes even if the peer has affordable socket buffers available. This causes small window
sizes and creates a performance ceiling for large data transfers. Though not included in this
chart, no clear performance difference is observed for small data (less than 4Kbytes) transfer.
Figure 4-16 the comparison with socket buffer 4Kbytes and 132 bytes
4.7.5 Additional TCP/IP tuning
There are many other configuration options which may increase or decrease network
performance. The parameters we describe below may help to prevent a decrease in network
performance. The following sysctl commands are used to change these parameters.
performance. The parameters we describe below may help to prevent a decrease in network
performance. The following sysctl commands are used to change these parameters.
Tuning IP and ICMP behavior
Disabling the following parameters prevents a cracker from using a spoofing attack against
the IP address of the server:
the IP address of the server:
sysctl -w net.ipv4.conf.eth0.accept_source_route=0
tran rate per sec by recv size
0
500
1000
1500
2000
2500
3000
3500
4000
1024 2048 4096 8192 16384 32768 65536 1E+05 3E+05 5E+05
Local socket buffer size
tr
an
s ra
te
p
e
r s
e
c
16Kbytes (rmem,wmem=132K)
32Kbytes (rmem,wmem=132K)
64Kbytes (rmem,wmem=132K)
128Kbytes (rmem,wmem=132K)
16Kbytes (wmem,rmem=4k)
32Kbytes (wmem,rmem=4k)
64Kbytes (wmem,rmem=4k)
128Kbytes (wmem,rmem=4k)
32Kbytes (rmem,wmem=132K)
64Kbytes (rmem,wmem=132K)
128Kbytes (rmem,wmem=132K)
16Kbytes (wmem,rmem=4k)
32Kbytes (wmem,rmem=4k)
64Kbytes (wmem,rmem=4k)
128Kbytes (wmem,rmem=4k)
Response data size
performance
decline observed by
small socket (Local
socket buffer size is
limited to 8Kbytes)
decline observed by
small socket (Local
socket buffer size is
limited to 8Kbytes)