On Fri, Mar 20, 2026 at 8:11 PM Joe Damato <joe@dama.to> wrote:
>
> Greetings:
>
> This series extends net/tso to add a data structure and some helpers allowing
> drivers to DMA map headers and packet payloads a single time. The helpers can
> then be used to reference slices of shared mapping for each segment. This
> helps to avoid the cost of repeated DMA mappings, especially on systems which
> use an IOMMU. N per-packet DMA maps are replaced with a single map for the
> entire GSO skb. As of v3, the series uses the DMA IOVA API (as suggested by
> Leon [1]) and provides a fallback path when an IOMMU is not in use. The DMA
> IOVA API provides even better efficiency than the v2; see below.
>
> The added helpers are then used in bnxt to add support for software UDP
> Segmentation Offloading (SW USO) for older bnxt devices which do not have
> support for USO in hardware. Since the helpers are generic, other drivers
> can be extended similarly.
>
> The v2 showed a ~4x reduction in DMA mapping calls at the same wire packet
> rate on production traffic with a bnxt device. The v3, however, shows a larger
> reduction of about ~6x at the same wire packet rate. This is thanks to Leon's
> suggestion of using the DMA IOVA API [1].
>
> Special care is taken to make bnxt ethtool operations work correctly: the ring
> size cannot be reduced below a minimum threshold while USO is enabled and
> growing the ring automatically re-enables USO if it was previously blocked.
>
> I've extended netdevsim to have support for SW USO, but I used
> tso_build_hdr/tso_build_data in netdevsim because I couldn't figure out if
> there was a way to test the DMA helpers added by this series. If anyone has
> suggestions, let me know. I think to test the DMA helpers you probably need
> to use real hardware.
>
> Since this v4 made minor updates to the python test (see below and patch 12
> changelog), I re-ran the test with both netdevsim and real bnxt hardware and
> the test passed.
>
> Thanks,
> Joe
>
Thanks Joe. Its nice work! I reviewed the series and added my Rb for
all patches except core changes (which btw also loog good to me, but I
think other experts may review)
> [1]: https://lore.kernel.org/netdev/20260316194419.GH61385@unreal/
>
> v4:
> - Fixed kdoc issues in patch 2. No functional change.
> - Added Pavan's Reviewed-by to patches 3, 4, and 5.
> - Fixed the issue Pavan (and the AI review) pointed out in patch 8. See
> patch changelog.
> - Added parentheses around gso_type check in patch 11 for clarity. No
> functional change.
> - Fixed python linter issues in patch 12. No functional change.
>
> v3: https://lore.kernel.org/netdev/20260318191325.1819881-1-joe@dama.to/
> - Converted from RFC to an actual submission.
> - Updated based on Leon's feedback to use the DMA IOVA API. See individual
> patches for update information.
>
> RFCv2: https://lore.kernel.org/netdev/20260312223457.1999489-1-joe@dama.to/
> - Some bugs were discovered shortly after sending: incorrect handling of the
> shared header space and a bug in the unmap path in the TX completion.
> Sorry about that; I was more careful this time.
> - On that note: this rfc includes a test.
>
> RFCv1: https://lore.kernel.org/netdev/20260310212209.2263939-1-joe@dama.to/
>
> Joe Damato (12):
> net: tso: Introduce tso_dma_map
> net: tso: Add tso_dma_map helpers
> net: bnxt: Export bnxt_xmit_get_cfa_action
> net: bnxt: Add a helper for tx_bd_ext
> net: bnxt: Use dma_unmap_len for TX completion unmapping
> net: bnxt: Add TX inline buffer infrastructure
> net: bnxt: Add boilerplate GSO code
> net: bnxt: Implement software USO
> net: bnxt: Add SW GSO completion and teardown support
> net: bnxt: Dispatch to SW USO
> net: netdevsim: Add support for SW USO
> selftests: drv-net: Add USO test
>
> drivers/net/ethernet/broadcom/bnxt/Makefile | 2 +-
> drivers/net/ethernet/broadcom/bnxt/bnxt.c | 190 +++++++++---
> drivers/net/ethernet/broadcom/bnxt/bnxt.h | 33 +++
> .../net/ethernet/broadcom/bnxt/bnxt_ethtool.c | 19 +-
> drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c | 236 +++++++++++++++
> drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h | 31 ++
> drivers/net/netdevsim/netdev.c | 100 ++++++-
> include/linux/skbuff.h | 11 +
> include/net/tso.h | 61 ++++
> net/core/tso.c | 273 ++++++++++++++++++
> tools/testing/selftests/drivers/net/Makefile | 1 +
> tools/testing/selftests/drivers/net/uso.py | 96 ++++++
> 12 files changed, 1013 insertions(+), 40 deletions(-)
> create mode 100644 drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c
> create mode 100644 drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h
> create mode 100755 tools/testing/selftests/drivers/net/uso.py
>
>
> base-commit: 9f4960b94f1a044f76da98a765d6cbd294c22c92
> --
> 2.52.0
>