On Tue, Feb 4, 2025 at 10:06 AM Stanislav Fomichev <stfomichev@xxxxxxxxx> wrote: > > On 02/04, Mina Almasry wrote: > > On Tue, Feb 4, 2025 at 4:32 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > > > > > On 2/3/25 11:39 PM, Mina Almasry wrote: > > > > The TX path had been dropped from the Device Memory TCP patch series > > > > post RFCv1 [1], to make that series slightly easier to review. This > > > > series rebases the implementation of the TX path on top of the > > > > net_iov/netmem framework agreed upon and merged. The motivation for > > > > the feature is thoroughly described in the docs & cover letter of the > > > > original proposal, so I don't repeat the lengthy descriptions here, but > > > > they are available in [1]. > > > > > > > > Sending this series as RFC as the winder closure is immenient. I plan on > > > > reposting as non-RFC once the tree re-opens, addressing any feedback > > > > I receive in the meantime. > > > > > > I guess you should drop this paragraph. > > > > > > > Full outline on usage of the TX path is detailed in the documentation > > > > added in the first patch. > > > > > > > > Test example is available via the kselftest included in the series as well. > > > > > > > > The series is relatively small, as the TX path for this feature largely > > > > piggybacks on the existing MSG_ZEROCOPY implementation. > > > > > > It looks like no additional device level support is required. That is > > > IMHO so good up to suspicious level :) > > > > > > > It is correct no additional device level support is required. I don't > > have any local changes to my driver to make this work. I think Stan > > on-list was able to run the TX path (he commented on fixes to the test > > but didn't say it doesn't work :D) and one other person was able to > > run it offlist. > > For BRCM I had shared this: https://lore.kernel.org/netdev/ZxAfWHk3aRWl-F31@mini-arch/ > I have similar internal patch for mlx5 (will share after RX part gets > in). I agree that it seems like gve_unmap_packet needs some work to be more > careful to not unmap NIOVs (if you were testing against gve). Hmm. I think you're right. We ran into a similar issue with the RX path. The RX path worked 'fine' on initial merge, but it was passing dmabuf dma-addrs to the dma-mapping API which Jason later called out to be unsafe. The dma-mapping API calls with dmabuf dma-addrs will boil down into no-ops for a lot of setups I think which is why I'm not running into any issues in testing, but upon closer look, I think yes, we need to make sure the driver doesn't end up passing these niov dma-addrs to functions like dma_unmap_*() and dma_sync_*(). Stan, do you run into issues (crashes/warnings/bugs) in your setup when the driver tries to unmap niovs? Or did you implement these changes purely for safety? Let me take a deeper look here and suggest something for the next version. I think we may indeed need the driver to declare that it can handle niovs in the TX path correctly (i.e. not accidentally pass niov dma-addrs to the dma-mapping API). -- Thanks, Mina
