Chapter 4. Tuning the operating system 135
Draft Document for Review May 4, 2007 11:35 am 4285ch04.fm
Figure 4-20 CPU usage improvement by offloading
However, a slight performance degradation is observed in using offloading (Figure 4-21). The
processing of checksums for such a high packet rate is a significant load on certain LAN
adapter processors. As the packet size gets larger, fewer packets per second are being
generated (because it takes a longer time to send and receive all that data) and it is prudent
to offload the checksum operation on to the adapter.
Figure 4-21 Throughput degradation by offloading
cpu usage improvement - default vs offload off
0
1
2
3
4
5
6
7
8
1 16 128 1024 1460 4096 16384 32768 65536 131072
recv data size
cpu usage improvement (%)
2048
4096
8192
16384
32768
65536
131070
262144
socket size
(bytes)
Throughput degradation ratio
default vs offload by socket size
0.82
0.84
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
1.0 2
1 16 128 1024 1460 4096 16384 32768 65536 1E+05
recv data size
10 2 4
2048
4096
8192
16384
32768
65536
13 10 7 0
262144
socket size
(bytes)
