[ovs-dev] question about dp_packet lifetime

[Alessandro Rosetti]

Hi Darrell,

I'm developing netmap support for my thesis and I hope it will make it for
OVS 2.10.
In the next days I'm going to post the first prototype patch that is almost
ready

Thanks to you,
Alessandro

On 19 Mar 2018 9:26 pm, "Darrell Ball" <dlu998 at gmail.com> wrote:

> Hi Alessandro
>
> I also think this would be interesting.
> Is netmap integration being actively being worked on for OVS 2.10 ?
>
> Thanks Darrell
>
> On Wed, Feb 7, 2018 at 9:19 AM, Ilya Maximets <i.maximets at samsung.com>
> wrote:
>
>> > Hi,
>>
>> Hi, Alessandro.
>>
>> >
>> >   My name is Alessandro Rosetti, and I'm currently adding netmap
>> support to
>> > ovs, following an approach similar to DPDK.
>>
>> Good to know that someone started to work on this. IMHO, it's a good idea.
>> I also wanted to try to implement this someday, but had no much time.
>>
>> >
>> > I've created a new netdev: netdev_netmap that uses the pmd
>> infrastructure.
>> > The prototype I have seems to work fine (I still need to tune
>> performance,
>> > test optional features, and test more complex topologies.)
>>
>> Cool. Looking forward for your RFC patch-set.
>>
>> >
>> > I have a question about the lifetime of dp_packets.
>> > Is there any guarantee that the dp_packets allocated in a receive
>> callback
>> > (e.g. netdev_netmap_rxq_recv) are consumed by OVS (e.g. dropped,
>> cloned, or
>> > sent to other ports) **before** a subsequent call to the receive
>> callback
>> > (on the same port)?
>> > Or is it possible for dp_packets to be stored somewhere (e.g. in an OVS
>> > internal queue) and live across subsequent invocations of the receive
>> > callback that allocated them?
>>
>> I think that there was never such a guarantee, but recent changes in
>> userspace
>> datapath completely ruined this assumption. I mean output packet batching
>> support.
>>
>> Please refer the following commits for details:
>> 009e003 2017-12-14 | dpif-netdev: Output packet batching.
>> c71ea3c 2018-01-15 | dpif-netdev: Time based output batching.
>> 00adb8d 2018-01-15 | docs: Describe output packet batching in DPDK guide.
>>
>> >
>> > I need to know if this is the case to check that my current prototype is
>> > safe.
>> > I use per-port pre-allocation of dp_packets, for maximum performance.
>> I've
>> > seen that DPDK uses its internal allocator to allocate and deallocate
>> > dp_packets, but netmap does not expose one.
>> > Each packet received with netmap is created as a new type dp_packet:
>> > DPBUF_NETMAP. The data points to a netmap buffer (preallocated by the
>> > kernel).
>> > When I receive data (netdev_netmap_rxq_recv) I reuse the dp_packets,
>> > updating the internal pointer and a couple of additional informations
>> > stored inside the dp_packet.
>> > When I have to send data I use zero copy if dp_packet is DPBUF_NETMAP
>> and
>> > copy if it's not.
>> >
>> > Thanks for the help!
>> > Alessandro.
>>
>>
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>
>