Eric W. Biederman wrote:
> Daniel Lezcano <dlezcano@fr.ibm.com> writes:
> 
> 
>>Benjamin Thery and I we were looking at this.
>>For the moment we are investigating if there is IP fragmentation between the
>>eth0 and the pair devices.
>>The profiling shows us "pskb_expand_head" and "csum_partial_copy_generic"
>>functions have the bigger CPU usage when we are inside a container.
> 
> 
> Hmm.  Interesting hypothesis.  I do know I haven't finished the IP fragment
> support so there may be an issue there.  Although generally especially with
> TCP fragments are not generated.  How are you thinking fragmentation would
> be involved?

I'm not sure I fully understand the test and details of the thread,
but still...

if network device inside container has MTU higher then eth0 outside the container,
then packets will get fragmented.
First time to MTU1 inside container and refragmented to MTU2
outside the container. At least this is the reason we use ethernet MTU
on venet devices in OpenVZ - to avoid framentation.

Thanks,
Kirill

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