netdev - Re: [RFC v2 bpf-next 2/7] drivers: net: turn on XDP features

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Message-ID: <Y8cTKOmCBbMEZK8D@sleipner.dyn.berto.se>
Date:   Tue, 17 Jan 2023 22:29:12 +0100
From:   Niklas Söderlund 
        <niklas.soderlund@...igine.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, davem@...emloft.net,
        kuba@...nel.org, hawk@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, toke@...hat.com, memxor@...il.com,
        alardam@...il.com, saeedm@...dia.com, anthony.l.nguyen@...el.com,
        gospo@...adcom.com, vladimir.oltean@....com, nbd@....name,
        john@...ozen.org, leon@...nel.org, simon.horman@...igine.com,
        aelior@...vell.com, christophe.jaillet@...adoo.fr,
        ecree.xilinx@...il.com, mst@...hat.com, bjorn@...nel.org,
        magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
        intel-wired-lan@...ts.osuosl.org, lorenzo.bianconi@...hat.com
Subject: Re: [RFC v2 bpf-next 2/7] drivers: net: turn on XDP features

Hi Lorenzo and Marek,

Thanks for your work.

On 2023-01-14 16:54:32 +0100, Lorenzo Bianconi wrote:

[...]

> 
> Turn 'hw-offload' feature flag on for:
>  - netronome (nfp)
>  - netdevsim.

Is there a definition of the 'hw-offload' written down somewhere? From 
reading this series I take it is the ability to offload a BPF program?  
It would also be interesting to read documentation for the other flags 
added in this series.

[...]

> diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c 
> b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> index 18fc9971f1c8..5a8ddeaff74d 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> @@ -2529,10 +2529,14 @@ static void nfp_net_netdev_init(struct nfp_net *nn)
>  	netdev->features &= ~NETIF_F_HW_VLAN_STAG_RX;
>  	nn->dp.ctrl &= ~NFP_NET_CFG_CTRL_RXQINQ;
>  
> +	nn->dp.netdev->xdp_features = NETDEV_XDP_ACT_BASIC |
> +				      NETDEV_XDP_ACT_HW_OFFLOAD;

If my assumption about the 'hw-offload' flag above is correct I think 
NETDEV_XDP_ACT_HW_OFFLOAD should be conditioned on that the BPF firmware 
flavor is in use.

    nn->dp.netdev->xdp_features = NETDEV_XDP_ACT_BASIC;

    if (nn->app->type->id == NFP_APP_BPF_NIC)
        nn->dp.netdev->xdp_features |= NETDEV_XDP_ACT_HW_OFFLOAD;

> +
>  	/* Finalise the netdev setup */
>  	switch (nn->dp.ops->version) {
>  	case NFP_NFD_VER_NFD3:
>  		netdev->netdev_ops = &nfp_nfd3_netdev_ops;
> +		nn->dp.netdev->xdp_features |= NETDEV_XDP_ACT_XSK_ZEROCOPY;
>  		break;
>  	case NFP_NFD_VER_NFDK:
>  		netdev->netdev_ops = &nfp_nfdk_netdev_ops;

This is also a wrinkle I would like to understand. Currently NFP support 
zero-copy on NFD3, but not for offloaded BPF programs. But with the BPF 
firmware flavor running the device can still support zero-copy for 
non-offloaded programs.

Is it a problem that the driver advertises support for both 
hardware-offload _and_ zero-copy at the same time, even if they can't be 
used together but separately?

-- 
Kind Regards,
Niklas Söderlund