Re: [Xen-users] Bandwidth between VMs on Xen

[Jaya Dhanesh <jaya.dhanesh@xxxxxxxxxxxx>]

There is a requirement to send pkts of size 4k. I was testing with 1500 
pkt size
On 01/17/2014 02:53 PM, Ian Campbell wrote:
> On Fri, 2014-01-17 at 13:56 +0530, Jaya Dhanesh wrote:
> > I am sending packets for size of 1500 bytes. For 1500, shouldn't it work
> > fine?
> And are you sure the kernel isn't coalesing those into 4096 byte chunks?
> If you are sending 1500 byte packets why are you messing with the MTU at
> all?
>
> > On 01/13/2014 04:46 PM, Ian Campbell wrote:
> > > On Mon, 2014-01-13 at 16:39 +0530, Jaya Dhanesh wrote:
> > > > Hi,
> > > >
> > > > I created 2 vm and connected them using a bridge. The bridge was
> > > > created using brctl command.
> > > > I set the mtu of the interface in the vm and the bridge to 4096. When
> > > > I tried to copy an image from one vm to another it was very slow and
> > > > the rate was 30 kbps. But when the mtu was reduced to 1500, the rate
> > > > increased to 3 mbps.  How does an decrease in the mtu increases the
> > > > transfer speed?
> > > Once you add the Ethernet headers every frame is taking just over 1
> > > page, wasting most of the second one. It perhaps also depends on the
> > > size of packets your test is generating.
> > >
> > > 4096 is an unusual MTU I think, typical values are 1500 and 9000.
> > >
> > > Ian.


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