IBM REDP-4285-00 User Manual
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.
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
cp
u
u
sag
e im
p
ro
vem
en
t (
%
)
2048
4096
8192
16384
32768
65536
131070
262144
socket size
(bytes)
(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
1.02
1
16
128
1024
1460
4096
16384 32768 65536
1E+05
recv d at a siz e
1024
2048
4096
8192
16384
32768
65536
131070
262144
2048
4096
8192
16384
32768
65536
131070
262144
socket size
(bytes)
(bytes)