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

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Date:   Thu, 3 Jun 2021 00:52:38 +0000
From:   "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>
To:     "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC:     "bjorn@...nel.org" <bjorn@...nel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH intel-next 2/2] ice: introduce XDP Tx fallback path

On Tue, 2021-06-01 at 13:32 +0200, Maciej Fijalkowski wrote:
> 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@...el.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,
Tony

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