Re: [Xen-devel] [PATCH V6 net-next 0/5] xen-net{back, front}: Multiple transmit and receive queues

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-03-14 at 16:10 +0000, Ian Campbell wrote:
> On Mon, 2014-03-03 at 11:47 +0000, Andrew J. Bennieston wrote:
> > This patch series implements multiple transmit and receive queues (i.e.
> > multiple shared rings) for the xen virtual network interfaces.
> > 
> > The series is split up as follows:
> >  - Patches 1 and 3 factor out the queue-specific data for netback and
> >     netfront respectively, and modify the rest of the code to use these
> >     as appropriate.
> >  - Patches 2 and 4 introduce new XenStore keys to negotiate and use
> >    multiple shared rings and event channels, and code to connect these
> >    as appropriate.
> >  - Patch 5 documents the XenStore keys required for the new feature
> >    in include/xen/interface/io/netif.h
> > 
> > All other transmit and receive processing remains unchanged, i.e. there
> > is a kthread per queue and a NAPI context per queue.
> > 
> > The performance of these patches has been analysed in detail, with
> > results available at:
> > 
> > http://wiki.xenproject.org/wiki/Xen-netback_and_xen-netfront_multi-queue_performance_testing
> > 
> > To summarise:
> >   * Using multiple queues allows a VM to transmit at line rate on a 10
> >     Gbit/s NIC, compared with a maximum aggregate throughput of 6 Gbit/s
> >     with a single queue.
> >   * For intra-host VM--VM traffic, eight queues provide 171% of the
> >     throughput of a single queue; almost 12 Gbit/s instead of 6 Gbit/s.
> 
> From the graphs it looks like 8 queues doesn't offer that much over 4
> and the bulk of the improvement comes from going to just 2 queues.
> 
> Any idea what the bottleneck is? i.e. why does the graph flatten so
> soon?

It's going offbox over a 0G link isn't it, so ignore me.

> 
> >   * There is a corresponding increase in total CPU usage, i.e. this is a
> >     scaling out over available resources, not an efficiency improvement.
> 
> corresponding to the number of queues or the throughput improvement?
> i.e. is it 8x or 1.71x with 8 queues?
> 
> Ian.
> 
> 
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