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

From: Luke Gorrie
Subject: Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU for userspace ethernet I/O
Date: Tue, 28 May 2013 16:42:02 +0200

On 28 May 2013 13:53, Michael S. Tsirkin <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.

Today I really am statically provisioning a CPU core using "linux isolcpus=..." boot option, but maybe e.g. scheduling with realtime priority would work too and free up some spare cycles for running VMs.

I am hoping that administrators will feel that dedicating ~6.25% total CPU (one core out of 16) for networking will be OK.

Remains to be seen whether we can really deliver this kind of performance with a mix of phsical NICs and VMs, but that's the design goal.

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