Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU for userspace ethernet I/O

[Julian Stecklina <jsteckli@os.inf.tu-dresden.de>]

On 05/28/2013 04:42 PM, Luke Gorrie wrote:
> On 28 May 2013 13:53, Michael S. Tsirkin <mst@redhat.com
> <mailto:mst@redhat.com>> wrote:
> 
>     Yes, you can maybe trade some of this latency for power/CPU cycles by
>     aggressive polling.  Doing this in a way that does not waste a lot of
>     power would be tricky.
> 
> 
> For what it's worth, here is my mental model right now:
> 
> Administrator budgets one CPU core for network I/O (VM and NIC).
> Switch uses that CPU to deliver sufficient speed (e.g. 10 M packets/sec
> ~ 40Gbps).
> Switch uses micro-sleeps to cut cpu usage to ~ 1% in idle periods.

With virtio the backend can decide whether it wants to be notified by
the client. If you disable all notifications you are in polling mode. If
your backend/switch doesn't find anything to do it can reenable
notifications and block. Thus you would naturally revert to non-polling
mode, when the network load is low.

Julian