Monitoring Queue Thresholds

Purpose

Display the color-based thresholds for queues on each egress slot.

Showing queue thresholds by queue profile shows buffer memory information for each queue profile and, within that profile, shows the thresholds for each region.

In addition, showing queue thresholds by region organizes the buffer memory information by queue region and, within each region, shows the buffer allocations for each queue profile.

Action

To display the color-based queue thresholds for each of the 2000 video queues when 8000 total queues are configured:

host1#show qos queue-thresholds egress-slot 9 queue-profile video

queue-profile video 2000 queues
                                                       total
          egress     exceeded  conformed  committed  committed
region    memory      length    length     length     memory
------  -----------  --------  ---------  ---------  ---------
  0       0MB - 4MB     34944      69888     139648  279296000
  1       4MB - 8MB     24448      48896      97792  195584000
  2      8MB - 12MB     14080      28032      55936  111872000
  3     12MB - 16MB      7040      14080      28032   56064000
  4     16MB - 20MB      5248      10496      20992   41984000
  5     20MB - 24MB      1280       2560       5120   10240000
  6     24MB - 28MB      1152       2176       4224    8448000
  7     28MB - 32MB       896       1792       3456    6912000

As shown, when all of the egress memory in use is between 0 MB and 4 MB, each video queue can queue 139,648 bytes of committed traffic. Because the default conformed fraction is 50 percent and the default exceeded fraction is 25 percent, half of the committed length, or 69,888 bytes, can be queued before conformed traffic is dropped, and one quarter of the committed length, or 34,944 bytes, can be queued before exceeded traffic is dropped. While memory fills, the video queues are given progressively smaller amounts of memory. For example, when 28 to 32 MB of buffer memory is in use, each video queue is limited to 3456 bytes. While memory fills beyond the last region, all frames are dropped except control traffic, until the queues are drained and memory usage falls back into one of the regions.

To display the router’s memory management:

host1#show qos queue-thresholds egress-slot 9 region 0
region 0 (0MB - 4MB) oversubscription 3330%
                                                        total
               exceeded  conformed  committed  queue  committed
queue-profile   length    length     length    count   memory
-------------  --------  ---------  ---------  -----  ---------
default           34944      69888     139648   2000  279296000
video             34944      69888     139648   2000  279296000
multicast         34944      69888     139648   2000  279296000
internet          34944      69888     139648   2000  279296000

Static and dynamic oversubscription determines that when 8000 queues are configured and 0–4 MB of egress buffer memory is in use, memory is oversubscribed by 3330 percent. If significantly fewer queues are configured, there is less oversubscription. This example illustrates static oversubscription.

Because all of the queues in Example 2 use default queue profiles, all queues have the same lengths. Each queue is allocated 139,648 bytes of committed buffer memory when operating within this region. This allocation allows active queues to burst traffic by using memory that is unused by quiescent queues. This example illustrates dynamic oversubscription, which is based on the assumption that when a large number of queues is configured, only a fraction of the queues is active at a given time. While more queues become active, memory fills and spills into another region. When this occurs, queues are given progressively smaller queue limits.

In memory regions 1 through 5, queue limits are progressively reduced. In region 6, memory is strictly partitioned among queues.

To display oversubscription in region 6:

host1#show qos queue-thresholds egress-slot 9 region 6
region 6 (24MB - 28MB) oversubscription 100%
                                                        total
               exceeded  conformed  committed  queue  committed
queue-profile   length    length     length    count   memory
-------------  --------  ---------  ---------  -----  ---------
default            1152       2176       4224   2000    8448000
video              1152       2176       4224   2000    8448000
multicast          1152       2176       4224   2000    8448000
internet           1152       2176       4224   2000    8448000

Oversubscription is 100 percent. When 24–28 MB of the memory is in use, there is no oversubscription of egress buffer memory; 32 MB of the 32-MB memory is allocated. In Example 3, each of the 8000 egress queues is given a queue of 4224 bytes, for a total of 16 MB.

If memory continues to fill into region 7, egress buffer memory is undersubscribed, allowing control traffic to flow within the router. As shown in Example 4, when operating in region 7, only 80 percent of the 32-MB memory is allocated.

To display oversubscription in region 7:

host1#show qos queue-thresholds egress-slot 9 region 7
region 7 (28MB - 32MB) oversubscription 80%
                                                        total
               exceeded  conformed  committed  queue  committed
queue-profile   length    length     length    count   memory
-------------  --------  ---------  ---------  -----  ---------
default             896       1792       3456   2000    6912000
video               896       1792       3456   2000    6912000
multicast           896       1792       3456   2000    6912000
internet            896       1792       3456   2000    6912000

Region 7 has 2000 IP users, each with four queues. Each of the four queues use default queue profiles. 

To display the queue thresholds in the multicast queue profile:

host1#show qos queue-thresholds egress-slot 9 queue-profile multicast
queue-profile multicast 2000 queues
                                                       total
          egress     exceeded  conformed  committed  committed
region    memory      length    length     length     memory
------  -----------  --------  ---------  ---------  ---------
  0       0MB - 4MB      5120      10112      20096   40192000
  1       4MB - 8MB      5120      10112      20096   40192000
  2      8MB - 12MB      5120      10112      20096   40192000
  3     12MB - 16MB      5120      10112      20096   40192000
  4     16MB - 20MB      5120      10112      20096   40192000
  5     20MB - 24MB      1280       2560      10112   20224000
  6     24MB - 28MB      1152       2176       4224    8448000
  7     28MB - 32MB       896       1792       3456    6912000

The multicast queue profile is configured with a committed length of 10,000 minimum and 20,000 maximum. When in regions 0–4, these queues would normally get more memory than the 20,000 byte maximum requested. In this case, the queue is limited to the maximum, and any excess memory is redistributed to other queues. Region 5 does not have enough memory to honor the 20,000-byte maximum requested.

Although a 20,000 byte maximum was requested, the router provisions memory in 128 byte blocks, rounded up or down per each request; 20,096 bytes is 157 blocks of 128 bytes.

In region 6, memory is strictly partitioned, and neither the minimum nor maximum request is honored. Instead, each multicast queue is given a fair share of the queue length so that aggressive bandwidth consumers cannot starve out moderate traffic consumers.

In region 7, memory is underprovisioned to allow queues to drain and to avoid starvation that occurs when egress buffer memory fills completely.

To display the queue thresholds for video queues:

host1#show qos queue-thresholds egress-slot 9 region 0
region 0 (0MB - 4MB) oversubscription 3330%
                                                        total
               exceeded  conformed  committed  queue  committed
queue-profile   length    length     length    count   memory
-------------  --------  ---------  ---------  -----  ---------
default           33664      67328     134656   2000  269312000
video             67328     134656     269184   2000  538368000
multicast          5120      10112      20096   2000   40192000
internet          33664      67328     134656   2000  269312000

You can configure video queues with a buffer weight of 16 and Internet and multicast queues with a buffer weight of 8 to ensure that video queues get to queue twice as much traffic as Internet and multicast queues.

Meaning

Table 36 lists the show qos queue-thresholds command output fields.

Related Documentation

• Configuring Queue Profiles to Manage Buffers and Thresholds
• show qos queue-thresholds