Open Stack

Mathieu Rohon wrote:

>I'm also very interested in scheduling VMs with Network requirement. This seems to be in the scope of NFV workgroup >[1].
>For instance, I think that scheduling should take into account bandwith/QoS requirement for a VM, or specific Nic
This falls in my area of interest as well. We’re working on making network quality of service guarantees by means of a combination of DSCP marking with a reservation database and separate hardware queues in physical network switches in order to ensure that the reservations granted don’t exceed the wire speed of the switches. Right now the only option if the total of requested reservations would exceed the wire speed of the switches is to deny reservations on the basis of “first come, first served” and “last come, doesn’t get served”, in other words simply issuing a failure response at reservation time to any tenants who attempt to make reservations after a particular switch port is maxed out (from a reservation perspective, not necessarily maxed out from an actual utilization perspective at any given moment.)
However, with the element of chance in VM scheduling to compute node, it’s possible that a tenant could get a deny response from the reservation server because their VM landed on a particularly reservation heavy rack. If their VM happened to land on a compute node in a different rack then there might well be plenty of excess bandwidth on that rack’s uplink. But our current implementation has no way to tell Nova or the tenant that a reservation that was denied could have been granted if the VM were relocated to a less network overloaded rack.

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