On Fri, Mar 21, 2025 at 10:39 AM Joe Damato [off-list ref] wrote:

On Fri, Mar 21, 2025 at 02:15:20AM +0000, Samiullah Khawaja wrote:

quoted

Add a new state to napi state enum:

- STATE_THREADED_BUSY_POLL
  Threaded busy poll is enabled/running for this napi.

Following changes are introduced in the napi scheduling and state logic:

- When threaded busy poll is enabled through sysfs it also enables
  NAPI_STATE_THREADED so a kthread is created per napi. It also sets
  NAPI_STATE_THREADED_BUSY_POLL bit on each napi to indicate that we are
  supposed to busy poll for each napi.

- When napi is scheduled with STATE_SCHED_THREADED and associated
  kthread is woken up, the kthread owns the context. If
  NAPI_STATE_THREADED_BUSY_POLL and NAPI_SCHED_THREADED both are set
  then it means that we can busy poll.

- To keep busy polling and to avoid scheduling of the interrupts, the
  napi_complete_done returns false when both SCHED_THREADED and
  THREADED_BUSY_POLL flags are set. Also napi_complete_done returns
  early to avoid the STATE_SCHED_THREADED being unset.

- If at any point STATE_THREADED_BUSY_POLL is unset, the
  napi_complete_done will run and unset the SCHED_THREADED bit also.
  This will make the associated kthread go to sleep as per existing
  logic.

Signed-off-by: Samiullah Khawaja <redacted>
---
 Documentation/ABI/testing/sysfs-class-net     |  3 +-
 Documentation/netlink/specs/netdev.yaml       | 12 ++-
 Documentation/networking/napi.rst             | 67 ++++++++++++-
 .../net/ethernet/atheros/atl1c/atl1c_main.c   |  2 +-
 drivers/net/ethernet/mellanox/mlxsw/pci.c     |  2 +-
 drivers/net/ethernet/renesas/ravb_main.c      |  2 +-
 drivers/net/wireless/ath/ath10k/snoc.c        |  2 +-
 include/linux/netdevice.h                     | 20 +++-
 include/uapi/linux/netdev.h                   |  6 ++
 net/core/dev.c                                | 93 ++++++++++++++++---
 net/core/net-sysfs.c                          |  2 +-
 net/core/netdev-genl-gen.c                    |  2 +-
 net/core/netdev-genl.c                        |  2 +-
 tools/include/uapi/linux/netdev.h             |  6 ++
 14 files changed, 188 insertions(+), 33 deletions(-)

I think this should be split into two patches which would ease
review and bisection:

  - First patch: introduce enum netdev_napi_threaded and
    NETDEV_NAPI_THREADED_ENABLE and the associated driver changes.

  - Second patch: introduce NETDEV_NAPI_THREADED_BUSY_POLL_ENABLE

Agreed. I will split this up and send again.

I'll have to take a closer look at all the changes here after I've
read the cover letter and have reproduced the results, but one issue
stands out:

quoted

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3c244fd9ae6d..b990cbe76f86 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

[...]

quoted

@@ -2432,7 +2442,7 @@ struct net_device {
      struct sfp_bus          *sfp_bus;
      struct lock_class_key   *qdisc_tx_busylock;
      bool                    proto_down;
-     bool                    threaded;
+     u8                      threaded;

Doesn't

Documentation/networking/net_cachelines/net_device.rst

Also need to be updated if you are changing the width of this field
from bool to u8?