> -----Original Message----- > From: Olivier MATZ [mailto:olivier.matz at 6wind.com] > Sent: Wednesday, November 12, 2014 1:06 PM > To: Ananyev, Konstantin; Yong Wang; Liu, Jijiang > Cc: dev at 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
