Re: [Xen-devel] [PATCH net-next v2 0/9] xen-netback: TX grant mappingwith SKBTX_DEV_ZEROCOPY instead of copy

[Zoltan Kiss]

On 16/12/13 06:32, annie li wrote:
> On 2013/12/13 7:48, Zoltan Kiss wrote:
> > A long known problem of the upstream netback implementation that on
> > the TX
> > path (from guest to Dom0) it copies the whole packet from guest memory
> > into
> > Dom0. That simply became a bottleneck with 10Gb NICs, and generally
> > it's a
> > huge perfomance penalty. The classic kernel version of netback used grant
> > mapping, and to get notified when the page can be unmapped, it used page
> > destructors. Unfortunately that destructor is not an upstreamable
> > solution.
> > Ian Campbell's skb fragment destructor patch series [1] tried to solve
> > this
> > problem, however it seems to be very invasive on the network stack's
> > code,
> > and therefore haven't progressed very well.
> > This patch series use SKBTX_DEV_ZEROCOPY flags to tell the stack it
> > needs to
> > know when the skb is freed up. That is the way KVM solved the same
> > problem,
> > and based on my initial tests it can do the same for us. Avoiding the
> > extra
> > copy boosted up TX throughput from 6.8 Gbps to 7.9 (I used a slower
> > Interlagos box, both Dom0 and guest on upstream kernel, on the same
> > NUMA node,
> > running iperf 2.0.5, and the remote end was a bare metal box on the
> > same 10Gb
> > switch)
> Sounds good.
> Is the TX throughput gotten between one vm and one bare metal box? or
> between multiple vms and bare metal? Do you have any test results with
> netperf?
One VM and a bare metal box. I've used only iperf.

Regards,

Zoli

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