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

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

Hi Thomas,

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Wednesday, November 12, 2014 1:41 PM
> To: Olivier MATZ; Ananyev, Konstantin; dev@dpdk.org
> Cc: Yong Wang
> Subject: Re: [dpdk-dev] [PATCH v8 10/10] app/testpmd:test VxLAN Tx checksum offload
> 
> 2014-11-12 14:05, Olivier MATZ:
> > 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.
> >
> > 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.
> 
> I feel this question is really important and we need more people to review
> the API. We'll also need more validation tests and performance checks with
> several use cases.
> 
> Release is already late and I'm not comfortable with such change now.
> The only chance to have dev_prep_tx() in 1.8 would be to quickly have a large
> consensus and some benchmarks in pipeline and run to completion models.
> 
> Conclusion: we should integrate TSO without dev_prep_tx (option 2 or 3) and
> then speed up dev & tests for dev_prep_tx(). This improvement for pipeline
> model could go in 2.0 if it's considered too short or risky for 1.8.
> Konstantin, could you be in charge of dev_prep_tx() works?

I can have a look at it in 2.0 timeframe.
Unless someone else is interested in doing it before that :)
Konstantin

> 
> Thanks for the good discussion
> --
> Thomas