Re: [dpdk-dev] [PATCH v4] net/af_packet: reinsert the stripped vlan tag

[Tudor Cornea <tudor.cornea@gmail.com>]

Hi Ferruh,

 Also driver was already working with VLAN, the change is VLAN is not
> force stripped anymore.


 Agreed. It makes more sense to inform the users that the default behavior
of the PMD has changed w.r.t VLAN stripping.

I have updated the patch

On Thu, 30 Sept 2021 at 11:14, Ferruh Yigit <ferruh.yigit@intel.com> wrote:

> On 9/29/2021 3:08 PM, Tudor Cornea wrote:
> > The af_packet pmd driver binds to a raw socket and allows
> > sending and receiving of packets through the kernel.
> >
> > Since commit [1], the kernel strips the vlan tags early in
> > __netif_receive_skb_core(), so we receive untagged packets while
> > running with the af_packet pmd.
> >
> > Luckily for us, the skb vlan-related fields are still populated from the
> > stripped vlan tags, so we end up having all the information
> > that we need in the mbuf.
> >
> > Having the pmd driver support DEV_RX_OFFLOAD_VLAN_STRIP allows the
> > application to control the desired vlan stripping behavior,
> > until we have a way to describe offloads that can't be disabled by
> > pmd drivers.
> >
> > This patch will cause a change in the default way that the af_packet
> > pmd treats received vlan-tagged frames. While previously, the
> > application was required to check the PKT_RX_VLAN_STRIPPED flag, after
> > this patch, the pmd will re-insert the vlan tag transparently to the
> > user, unless the DEV_RX_OFFLOAD_VLAN_STRIP is enabled in
> > rxmode.offloads.
> >
> > I've attempted a preliminary benchmark to understand if the change could
> > cause a sizable performance hit.
> >
> > Setup:
> > Two virtual machines running on top of an ESXi hypervisor
> >
> > Tx: DPDK app (running on top of vmxnet3 PMD)
> > Rx: af_packet (running on top of a kernel vmxnet3 interface)
> > Packet size :68 (packet contains a vlan tag)
> >
> > Rates:
> > Tx - 1.419 Mpps
> > Rx (without vlan insertion) - 1227636 pps
> > Rx (with vlan insertion)    - 1220081 pps
> >
> > At a first glance, we don't seem to have a large degradation in terms
> > of packet rate.
> >
> > [1]
> https://github.com/torvalds/linux/commit/bcc6d47903612c3861201cc3a866fb604f26b8b2
> >
> > Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> >
> > ---
> > v4:
> > * Updated the af_packet documentation
> > v3:
> > * Updated release note and documentation
> > * Updated commit with performance measurements
> > v2:
> > * Added DEV_RX_OFFLOAD_VLAN_STRIP to rxmode->offloads
> > ---
> >  doc/guides/nics/af_packet.rst             |  5 +++++
> >  doc/guides/rel_notes/release_21_11.rst    |  4 ++++
> >  drivers/net/af_packet/rte_eth_af_packet.c | 12 ++++++++++++
> >  3 files changed, 21 insertions(+)
> >
> > diff --git a/doc/guides/nics/af_packet.rst
> b/doc/guides/nics/af_packet.rst
> > index efd6f1c..c87310b 100644
> > --- a/doc/guides/nics/af_packet.rst
> > +++ b/doc/guides/nics/af_packet.rst
> > @@ -65,3 +65,8 @@ framecnt=512):
> >  .. code-block:: console
> >
> >
> --vdev=eth_af_packet0,iface=tap0,blocksz=4096,framesz=2048,framecnt=512,qpairs=1,qdisc_bypass=0
> > +
> > +Features and Limitations of the af_packet PMD
> > +---------------------------------------------
> > +
> > +Af_packet PMD now works with VLAN's on Linux
>
> Thanks Tudor.
>
> I see this is suggested by Stephen, but I think 'now' is confusing in the
> driver
> guide. Also driver was already working with VLAN, the change is VLAN is not
> force stripped anymore.
>
> I think following part from your previous version is better, what do you
> think
> something like following?
> "
> The PMD will re-insert the VLAN tag transparently to the packet
> if the kernel strips it, as long as the ``DEV_RX_OFFLOAD_VLAN_STRIP`` is
> not
> enabled by application.
> "
>
> > diff --git a/doc/guides/rel_notes/release_21_11.rst
> b/doc/guides/rel_notes/release_21_11.rst
> > index ad7c1af..095fd5b 100644
> > --- a/doc/guides/rel_notes/release_21_11.rst
> > +++ b/doc/guides/rel_notes/release_21_11.rst
> > @@ -66,6 +66,10 @@ New Features
> >
> >    * Added rte_flow support for dual VLAN insert and strip actions.
> >
> > +* **Updated af_packet ethdev driver.**
> > +
> > +  * Added DEV_RX_OFFLOAD_VLAN_STRIP capability.
> > +
>
> I think change in the default behavior is more important in the release
> notes,
> again what do you think to have your following update here:
>
> "
> Default VLAN strip behavior changed. If previously,
> the vlan tag was stripped, if the application now requires the same
> behavior,
> it will need to configure ``DEV_RX_OFFLOAD_VLAN_STRIP``.
> "
>