Re: [PATCH intel-next 2/2] ice: introduce XDP Tx fallback path

On Thu, Jun 03, 2021 at 01:52:38AM +0100, Nguyen, Anthony L wrote:

On Tue, 2021-06-01 at 13:32 +0200, Maciej Fijalkowski wrote:

quoted

Under rare circumstances there might be a situation where a
requirement
of having a XDP Tx queue per core could not be fulfilled and some of
the
Tx resources would have to be shared between cores. This yields a
need
for placing accesses to xdp_rings array onto critical section
protected
by spinlock.

Design of handling such scenario is to at first find out how many
queues
are there that XDP could use. Any number that is not less than the
half
of a count of cores of platform is allowed. XDP queue count < cpu
count
is signalled via new VSI state ICE_VSI_XDP_FALLBACK which carries the
information further down to Rx rings where new ICE_TX_XDP_LOCKED is
set
based on the mentioned VSI state. This ring flag indicates that
locking
variants for getting/putting xdp_ring need to be used in fast path.

For XDP_REDIRECT the impact on standard case (one XDP ring per CPU)
can
be reduced a bit by providing a separate ndo_xdp_xmit and swap it at
configuration time. However, due to the fact that net_device_ops
struct
is a const, it is not possible to replace a single ndo, so for the
locking variant of ndo_xdp_xmit, whole net_device_ops needs to be
replayed.

It has an impact on performance (1-2 %) of a non-fallback path as
branches are introduced.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 drivers/net/ethernet/intel/ice/ice.h          | 37 +++++++++
 drivers/net/ethernet/intel/ice/ice_base.c     |  5 ++
 drivers/net/ethernet/intel/ice/ice_lib.c      |  4 +-
 drivers/net/ethernet/intel/ice/ice_main.c     | 76
++++++++++++++++++-
 drivers/net/ethernet/intel/ice/ice_txrx.c     | 62 ++++++++++++++-
 drivers/net/ethernet/intel/ice/ice_txrx.h     |  2 +
 drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 13 +++-
 7 files changed, 191 insertions(+), 8 deletions(-)

This isn't applying to next-queue/dev-queue. I believe it's becuase the
branch has the soon to be sent tracing patch from Magnus [1].

Thanks for a heads up Tony, I'll send rebased revision.

Thanks,
Tony

[1] https://patchwork.ozlabs.org/project/intel-wired-
lan/patch/20210510093854.31652-3-magnus.karlsson@gmail.com/