For some reason, Cisco decided to keep it hidden although it may be added to the next release. As of now use this command with caution, since it is hidden it is not supported in the configuration (yet).
Here is how you configure 'Active Latency Monitoring' on a Cisco Nexus 3548.
This is FILO latency so first in last byte out latency so you will not see ~ 230ns as promised by Cisco. If this was measuring FIFO latency then you might see the ~ 230ns per port latency. So the main thing is that you do a baseline trending and whenever there are spikes you can then calculate the difference and figure out the delay/latency.
Here is how to configure Active Latency Monitoring.
TestNex(config)#hardware profile latency monitor threshold-avg 1000000 threshold-max 2000000
You can set different threshold-avg and max to get syslog alerts.
These are the show commands to view the Active Latency Monitoring statistics.
TestNex# show hardware profile latency monitor summary Latency monitoring is an unsupported and untested feature, use at your own risk. All latency information provided is measured as FILO (First In Last Out). 11/24/2013 12:07:33 Device instance 0 Total Switch ============ 3s 30s 1hr All Time Min Latency (ns) 297 293 292 292 Max Latency (ns) 608 1957 2688 2688 Avg Latency (ns) 332 342 343 342 Std Deviation 23.95 8.31 0.75 0.73 Ethernet1/1 =========== 3s 30s 1hr All Time Min Latency (ns) 400 398 398 398 Max Latency (ns) 416 1935 2041 2041 Avg Latency (ns) 408 446 448 448 Std Deviation n/a 14.17 20.20 20.26
Interpreting this output for Ethernet1/1 - In the past 3 seconds, the minimum latency for all packets egressing the interface was ~ 400ns, the maximum was ~ 416ns and average latency for all packets ~ 408ns. It goes on to show you the 30s, the 1hr and All time. Although I am not sure what the 'All Time' means whether it keeps it for a day or just for 2 hours. These counters can be valuable to trend overtime, and analyze for spikes and for capacity planning.
There is also a way to get raw counters which will output much more granular statistics collected every 3 seconds.
TestNex# show hardware profile latency monitor raw interface Ethernet1/1 Latency monitoring is an unsupported and untested feature, use at your own risk. All latency information provided is measured as FILO (First In Last Out). 11/24/2013 12:15:11 Device instance 0 Format: timestamp ifindex fcnt min_latency max_latency avg_latency std_deviation 11/24/2013 12:15:08 0x1a000000 4 290 308 295 0.00 11/24/2013 12:15:05 0x1a000000 8 291 311 301 0.00 11/24/2013 12:15:02 0x1a000000 5 305 425 330 0.00
Many more articles to come so stay tuned.
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