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Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU

From: Julian Stecklina
Subject: Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU for userspace ethernet I/O
Date: Tue, 28 May 2013 17:33:45 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6

On 05/28/2013 04:42 PM, Luke Gorrie wrote:
> On 28 May 2013 13:53, Michael S. Tsirkin <address@hidden
> <mailto:address@hidden>> 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.


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