How to Measure Network Bandwidth and Latency with qperf

When building network servers, bandwidth determines the maximum load while latency limits the achievable QPS for request‑response protocols. Real‑world measurements often differ from theoretical values because of driver settings, switch hops, packet loss, protocol‑stack configuration, and physical link speed.

Installing qperf

qperf is included in the RHEL 6 distribution, so installation is straightforward:

yum install qperf

Basic usage

Run qperf without arguments on one host to start it in server mode: $ qperf On a second host, invoke qperf with the server’s address and the test name, e.g.: $ qperf 10.232.64.yyy tcp_bw tcp_lat conf The command returns bandwidth, latency, and CPU utilization for the TCP test, along with configuration details of both nodes.

Sample output

tcp_bw: bw = 118 MB/sec

tcp_lat: latency = 31.9 us

loc_node = xxx.sqa.cm4

loc_cpu = 16 Cores: Intel Xeon L5630 @ 2.13GHz

loc_os = Linux 2.6.32-131.21.1.tb477.el6.x86_64

loc_qperf = 0.4.6

rem_node = yyy.sqa.cm4

rem_cpu = 16 Cores: Intel Xeon L5630 @ 2.13GHz

rem_os = Linux 2.6.32-131.21.1.tb477.el6.x86_64

rem_qperf = 0.4.6

Advanced options – looping over a variable

qperf can repeat a test while varying a parameter using the -oo (or -loop) option: $ qperf -oo msg_size:1:64K:*2 10.232.64.yyy tcp_bw tcp_lat This runs the TCP bandwidth test for message sizes from 1 byte up to 64 KB, doubling each step. Sample results show bandwidth rising from 2.43 MB/s for 1 B messages to 118 MB/s for 64 KB messages, while latency remains low for small messages and grows sharply as the size approaches 1 KB.

Observations

The measurements reveal that bandwidth plateaus around 118 MB/s, and latency jumps dramatically when the packet size exceeds roughly 1 KB, providing useful thresholds for performance tuning.

Other protocols

Besides TCP, qperf can test RDMA, UDP, SCTP, and other common network transports, making it a versatile tool for network performance analysis.