Cisco Nexus 3548 Switch NX-OS Quality of Service Configuration Guide, Release 6.x
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- Updated:
- October 26, 2015
Chapter: Configuring Active Latency Monitoring
Configuring Active
Latency Monitoring
This chapter contains the following sections:
- Active Latency Monitoring Overview
- Active Latency Monitoring Guidelines and Limitations
- Configuring Active Latency Monitoring
- Show Examples for Active Latency Monitoring
Active Latency Monitoring Overview
Active Latency Monitoring provides a real-time view of the latency that is incurred by the packets while traveling through the switch on a per port basis. The latency measurement is FIFO measurement. Functionally, as soon as the packet enters the switch, the ASIC adds a timestamp to it. When it is scheduled to go out of the egress port, the egress port calculates the latency for each packet that is going out of that port based on current time and the ingress timestamp on the packet.
 Note | Active latency monitoring is currently not available for Cisco Nexus N3548 Series switches. This feature is only supported for Cisco Nexus N3548-X Series switches. |
Each egress port maintains the information in the frame count and the latency register, along with the minimum and maximum latency on that port. The software periodically reads the frame count (default 3 seconds) and the total latency to calculate the average latency per port. Based on per port latency information, the software calculates the average switch latency.
Active Latency Monitoring Guidelines and Limitations
Active Latency Monitoring has the following limitations and guidelines:
Configuring Active Latency Monitoring
To configure active latency monitoring, complete the following steps:
Note | The average or maximum latency threshold is in nanoseconds. The software sampling interval value is between 1 to 30 seconds. The default values for the parameters are: |
Show Examples for Active Latency Monitoring
See the following examples that provide a real-time view of the latency incurred by the packets:
switch# show hardware profile latency monitor summary
10/13/2015 06:55:58
Device instance 0
Total Switch
============
3s 30s 1hr All Time
Min Latency (ns) 390 375 n/a 369
Max Latency (ns) 775 1844 n/a 1950
Avg Latency (ns) 612 721 n/a 754
Std Deviation 205.24 117.23 n/a 69.17
Ethernet1/1
===========
3s 30s 1hr All Time
Min Latency (ns) 775 762 n/a 762
Max Latency (ns) 775 1757 n/a 1950
Avg Latency (ns) 775 838 n/a 870
Std Deviation n/a 83.87 n/a 100.93
<snip>
Ethernet1/13
============
3s 30s 1hr All Time
Min Latency (ns) 671 646 n/a 644
Max Latency (ns) 671 1844 n/a 1844
Avg Latency (ns) 671 736 n/a 740
Std Deviation n/a 100.16 n/a 93.76
switch# show hardware profile latency monitor summary detail
10/13/2015 06:57:00
Device instance 0
Format:
timestamp
ifindex
fcnt
min_latency
max_latency
avg_latency
10/13/2015 06:56:58
Ethernet1/1
fcnt 2
min_latency 565
max_latency 571
avg_latency 568
10/13/2015 06:56:55
Ethernet1/1
fcnt 1
min_latency 576
max_latency 576
avg_latency 576
10/13/2015 06:56:52
<snip>
Ethernet1/2
fcnt 0
min_latency 4294967295
max_latency 0
avg_latency 0
10/13/2015 06:56:55
Ethernet1/2
fcnt 0
min_latency 4294967295
max_latency 0
avg_latency 0
10/13/2015 06:56:52
switch# # show hardware profile latency monitor summary clear-timestamp
10/13/2015 06:56:31
Device instance 0
Egress Port Last Clear Timestamp
============================================
Total Switch 10/13/2015 06:54:35
Ethernet1/1 10/13/2015 06:54:35
Ethernet1/2 10/13/2015 06:54:35
<snip>
Ethernet1/47 10/13/2015 06:54:35
Ethernet1/48 10/13/2015 06:54:35
switch# show hardware profile latency monitor summary brief
10/13/2015 06:57:27
Device instance 0
Egress Port Avg Latency (ns)
========================================
Total Switch 769
Ethernet1/1 874
Ethernet1/2 1682
<snip>
Ethernet1/47 n/a
Ethernet1/48 n/a
switch# show hardware profile latency monitor summary sort
10/13/2015 06:57:34
Device instance 0
Egress Port Avg Latency (ns)
========================================
Ethernet1/2 1682
Ethernet1/5 1664
Ethernet1/1 871
Ethernet1/13 765
Ethernet1/6 507
Ethernet1/3 n/a
switch# show hardware profile latency monitor summary top
10/13/2015 06:57:44
Device instance 0
Egress Port Avg Latency (ns)
========================================
Ethernet1/2 1682
Ethernet1/5 1664
<snip>
Ethernet1/6 500
Ethernet1/3 n/a
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