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Hi, I am new using Iperf and might need some help in the
following characteristics of Iperf which I can’t understand. 1) When I
reduce the I/O Buffer Size “-l” option on the Server side to 64
bytes “-l 64” I see following things a. The
Transmission rate, per TCP stream for both “-P 1” ( 1 TCP stream) and
“-P 4” (4 TCP stream) are almost equal.
i.
Eg., Total transmission rate for
-P 1 is 108 Mbytes/sec
-P 4 is 108 *4 = 432 Mbytes/sec If the
total aggregate bandwidth is more than what an individual stream gets,
something is wrong
either with the network connections, OS TCP configuration or Window size
(http://dast.nlanr.net/Projects/Iperf/iperfdocs_1.7.0.php#tuningtcp).
I face this problem only for lower IO buffer sizes (> 1024B). Why is this anomaly
for small buffer sizes?
b. The CPU in
the send side is not compute bound as it is about 95% to 100% idle during the
small buffer size runs. Why doesn’t the application make use of the CPU
and increase in throughput? Any pointers to modify the code to increase
throughput capitalizing on the idle CPU cycles will be very helpful! Any help is greatly appreciated! Thanks in advance for the help, -Samson |