swaping ring slots between NIC ring and Host ring does not always success

[Luigi Rizzo]

On Fri, Jan 29, 2016 at 2:12 PM, Xiaoye Sun <Xiaoye.Sun at rice.edu> wrote:
> Hi Luigi,
>
> Thanks for your advice.
> I forgot to mention that I use the command "ethtool -L eth1 combined 1" to
> set the number of rings of the nic to 1.  The host also only has one ring.
> I understand the situation where the first tx ring is full so the bridge
> will swap the packets to the second tx ring and then the host/nic might
> drain either rings. But this is not the case in the experiment.

ok good to know that.

So if we have ruled out multiqueue and iommu, let's look at
the internal allocator and at bridge.c

1. are you running the most recent version of netmap ?
   Some older version (probably 1-2 years ago) had a bug
   in the buffer allocator and some buffers were allocated
   twice.

2. can you tweak your receiver.c to report some more info
   on how often you get out of sequence packets, how much
   out of sequence they are ?
   Also it would be useful to report gaps on the increasing side
   (i.e. new_seq != old_seq +1 )

3. can you tweak bridge.c so that it writes into the packet
   the netmap buffer indexes and slots on the rx and tx side,
   so when you detect a sequence error we can figure out
   where it is happening.
   Ideally you could also add the sequence number detection
   code in bridge.c so we can check whether the errors appear
   on the input or output sides.

cheers
luigi