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



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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