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

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Message-ID: <Y8ey7Sg3BcPfsU9d@sleipner.dyn.berto.se>
Date:   Wed, 18 Jan 2023 09:50:53 +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,

On 2023-01-18 00:45:44 +0100, Lorenzo Bianconi wrote:
> > 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?  
> 
> correct
> 
> > It would also be interesting to read documentation for the other flags 
> > added in this series.
> 
> maybe we can add definitions in Documentation/netlink/specs/netdev.yaml?
> 
> > 
> > [...]
> > 
> > > 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;
> 
> ack, I will fix it.

Thanks. I have just been informed from Yinjun Zhang that this check is 
not enough as this function is reused for VF where nn->app is not set. I 
think a better check would be

    if (nn->app && nn->app->type->id == NFP_APP_BPF_NIC)

Yinjun also informed me that you can make this code a bit neater by,

    s/nn->dp.netdev->xdp_features/netdev->xdp_features/

Thanks again for your work.

> 
> > 
> > > +
> > >  	/* 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?
> 
> xdp_features should export NIC supported features in the current
> configuration and it is expected they can be used concurrently.
> 
> Regards,
> Lorenzo
> 
> > 
> > -- 
> > Kind Regards,
> > Niklas Söderlund



-- 
Kind Regards,
Niklas Söderlund