netdev - RE: [Intel-wired-lan] [PATCH v7 intel-next 8/9] ice: introduce XDP

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Date:   Fri, 3 Sep 2021 06:50:43 +0000
From:   "Kuruvinakunnel, George" <george.kuruvinakunnel@...el.com>
To:     "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC:     "joamaki@...il.com" <joamaki@...il.com>,
        "Lobakin, Alexandr" <alexandr.lobakin@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "toke@...hat.com" <toke@...hat.com>,
        "bjorn@...nel.org" <bjorn@...nel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>
Subject: RE: [Intel-wired-lan] [PATCH v7 intel-next 8/9] ice: introduce XDP_TX
 fallback path

> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of Maciej
> Fijalkowski
> Sent: Thursday, August 19, 2021 5:30 PM
> To: intel-wired-lan@...ts.osuosl.org
> Cc: joamaki@...il.com; Lobakin, Alexandr <alexandr.lobakin@...el.com>;
> netdev@...r.kernel.org; toke@...hat.com; bjorn@...nel.org; kuba@...nel.org;
> bpf@...r.kernel.org; davem@...emloft.net; Karlsson, Magnus
> <magnus.karlsson@...el.com>
> Subject: [Intel-wired-lan] [PATCH v7 intel-next 8/9] ice: introduce XDP_TX fallback
> path
> 
> Under rare circumstances there might be a situation where a requirement of having
> XDP Tx queue per CPU could not be fulfilled and some of the Tx resources have
> to be shared between CPUs. This yields a need for placing accesses to xdp_ring
> inside a critical section protected by spinlock.
> These accesses happen to be in the hot path, so let's introduce the static branch
> that will be triggered from the control plane when driver could not provide Tx queue
> dedicated for XDP on each CPU.
> 
> Currently, the design that has been picked is to allow any number of XDP Tx
> queues that is at least half of a count of CPUs that platform has.
> For lower number driver will bail out with a response to user that there were not
> enough Tx resources that would allow configuring XDP. The sharing of rings is
> signalled via static branch enablement which in turn indicates that lock for xdp_ring
> accesses needs to be taken in hot path.
> 
> Approach based on static branch has no impact on performance of a non-fallback
> path. One thing that is needed to be mentioned is a fact that the static branch will
> act as a global driver switch, meaning that if one PF got out of Tx resources, then
> other PFs that ice driver is servicing will suffer. However, given the fact that HW
> that ice driver is handling has 1024 Tx queues per each PF, this is currently an
> unlikely scenario.
> 
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice.h          |  3 ++
>  drivers/net/ethernet/intel/ice/ice_lib.c      |  4 +-
>  drivers/net/ethernet/intel/ice/ice_main.c     | 53 ++++++++++++++++---
>  drivers/net/ethernet/intel/ice/ice_txrx.c     | 16 +++++-
>  drivers/net/ethernet/intel/ice/ice_txrx.h     |  1 +
>  drivers/net/ethernet/intel/ice/ice_txrx_lib.c |  7 ++-
>  6 files changed, 75 insertions(+), 9 deletions(-)
> 

Tested-by: George Kuruvinakunnel <george.kuruvinakunnel@...el.com>