Re: [dpdk-dev] [PATCH v8 10/10] app/testpmd:test VxLAN Tx checksum offload

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
> Sent: Wednesday, November 12, 2014 1:06 PM
> To: Ananyev, Konstantin; Yong Wang; Liu, Jijiang
> Cc: dev@dpdk.org; Thomas Monjalon
> Subject: Re: [dpdk-dev] [PATCH v8 10/10] app/testpmd:test VxLAN Tx checksum offload
> 
> Hi Konstantin,
> 
> On 11/12/2014 10:55 AM, Ananyev, Konstantin wrote:
> >>  From an API perspective, it looks a bit more complex to have to call
> >> dev_prep_tx() before sending the packets if they have been flagged
> >> for offload processing. But I admit I have no other argument. I'll be
> >> happy to have more comments from other people on the list.
> >>
> >> I'm sending a first version of the patchset now as it's ready, it does
> >> not take in account this comment, but I'm open to add it in a v2 if
> >> there is a consensus on this.
> >>
> >> Now, knowing that:
> >> - adding dev_prep_tx() will also concern hw checksum (TCP L4 checksum
> >>    already requires to set the TCP pseudo header checksum), so adding
> >>    this will change the API of an existing feature
> >> - TSO is a new feature expected for 1.8 (which should be out soon)
> >>
> >> Do you think we need to include this for 1.8 or can we postpone your
> >> proposition for after the 1.8 release?
> >
> > I'd say it would be good to have it done together with TSO feature.
> > About changing API: I think existing applications shouldn't be affected.
> > For existing PMDs/TX offloads we don't change  any rules what need to be filled by the app.
> > We just add a new function that can do that for user.
> > If the app fills required manually (as all apps have to do now) it would keep working as expected.
> 
> I agree, this proposition could work without changing the current
> applications.
> 
> > If you feel like it is too much work for 1.8 timeframe -
> > can we at least move fix_tcp_phdr_cksum() out of TX PMD as a temporary measure?
> > Let say create a function  get_ipv4_udptcp_checksum(struct rte_mbuf *m) (in librte_net ?).
> > It will calculate PSD checksum for both TSO and non-TSO case based on given mbuf flags/fields.
> > Then we can update testpmd/csumonly.c to use it.
> 
> I'm not sure having get_ipv4_udptcp_checksum() in librte_net would
> help. The value we have to set in the TCP checksum field depends on the
> PMD (altought only ixgbe is supported now). So, it would require
> another parameter <portid> and a new PMD eth_ops... which looks very
> similar to dev_prep_tx() (except that dev_prep_tx() can be bulked).
> I think a stack will not be able to call get_udptcp_checksum(m ,port)
> because it does not know the physical port at the time the packet is
> built. Moreover, calling a function through a pointer is more efficient
> when bulked. So I think the dev_prep_tx() you initially describe is
> a better answer to the problem.

Yes I understand that it might not be applicable for non-Intel NICs.
Though I thought it is ok as a temporary measure as right now we
support these offloads for Intel NICs only.
Basically my thought was what you proposed as option 3 below.
Why common function in librte_net?
So people don't need to write their own each time.
Plus as I remember all 3 Intel NIC types (ixgbe/igb/i40e) we support have similar 
requirements for what need to be set/calculated for these TX offloads.
So my thought was that having a common function might help to avoid code duplication in future,
If/when will implement dev_prep_tx(). 

> 
> I don't know what is the exact timeframe for 1.8, maybe Thomas can help
> on this? Depending on it, we have several options:
> 
> - implement dev_prep_tx() for 1.8 in the TSO series: this implies that
>    the community agrees on this new API. We need to check that it will
>    be faster in a pipeline model (I think this is obvious) but also that
>    it does not penalize the run-to-completion model: introducing another
>    function dev_prep_tx() can result in duplicated tests in the driver
>    (ex: test the offload flag values).
> 
> - postpone dev_prep_tx() or similar to next version and push the current
>    TSO patchset (including the comments done on the list). It does not
>    modify the current offload API, it provides the TSO feature on ixgbe
>    based on a similar API concept (set the TCP phdr cksum). The drawback
>    is a potential performance loss when using a pipeline model.
> 
> - another option that you may prefer is to bind the API behavior to
>    ixgbe (for 1.8): we can ask the application to set the pseudo-header
>    checksum without the IP len when doing TSO, as required by the ixgbe
>    driver. Then, for next release, we can think about dev_prep_tx(). The
>    drawback of this solution is that we may go back on this choice if the
>    dev_prep_tx() approach is not validated by the community.


My vote would be for option 3 then.

Thanks
Konstantin

> 
> 
> Regards,
> Olivier