Quality of Service (QoS) in Neutron - Notes in documentation regarding burst (80% BW)

[Arkady Shtempler]

We have two notes regarding burst value (80% BW) in documentation:

1) First Note
### The QoS implementation requires a burst value to ensure proper behavior of bandwidth limit rules in the Open vSwitch and Linux bridge agents. If you do not provide a value, it defaults to 80% of the bandwidth limit which works for typical TCP traffic.###

This note is in place here, as it coming after "openstack network qos rule create --type bandwidth-limit --max-kbps 3000 --max-burst-kbits 2400 --egress bw-limite"in previous" command, where burst value presents and that's OK.

2) Second Note
### Configuring the proper burst value is very important. If the burst value is set too low, bandwidth usage will be throttled even with a proper bandwidth limit setting. This issue is discussed in various documentation sources, for example in Juniper’s documentation. Burst value for TCP traffic can be set as 80% of desired bandwidth limit value. For example, if the bandwidth limit is set to 1000kbps then enough burst value will be 800kbit. If the configured burst value is too low, achieved bandwidth limit will be lower than expected. If the configured burst value is too high, too few packets could be limited and achieved bandwidth limit would be higher than expected. ###

How this note is related to previous command (openstack network set --qos-policy bw-limiter private), where QoS is associated to network? There is nothing about burst there?!

I think that both notes should be merged and placed where first one is located.

[Armando Migliaccio (armando-migliaccio)]

Good suggestion. The source documentation is available in [1]. If you are open to contributing a patch, you could consider tweaking the wording the way you see appropriate!

Many thanks!

[1] https://github.com/openstack/neutron/blob/master/doc/source/admin/config-qos.rst