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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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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