netdev - Re: [PATCH bpf-next v3 0/5] net: xdp: refactor XDP program queries

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Message-ID: <20190611102245.1565e742@cakuba.netronome.com>
Date:   Tue, 11 Jun 2019 10:22:45 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Björn Töpel <bjorn.topel@...el.com>
Cc:     Björn Töpel <bjorn.topel@...il.com>,
        ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        magnus.karlsson@...el.com, toke@...hat.com, brouer@...hat.com,
        bpf@...r.kernel.org, saeedm@...lanox.com
Subject: Re: [PATCH bpf-next v3 0/5] net: xdp: refactor XDP program queries

On Tue, 11 Jun 2019 09:24:41 +0200, Björn Töpel wrote:
> On 2019-06-11 00:24, Jakub Kicinski wrote:
> > On Mon, 10 Jun 2019 18:02:29 +0200, Björn Töpel wrote:  
> >> Jakub, what's your thoughts on the special handling of XDP offloading?
> >> Maybe it's just overkill? Just allocate space for the offloaded
> >> program regardless support or not? Also, please review the
> >> dev_xdp_support_offload() addition into the nfp code.  
> > 
> > I'm not a huge fan of the new approach - it adds a conditional move,
> > dereference and a cache line reference to the fast path :(
> > 
> > I think it'd be fine to allocate entries for all 3 types, but the
> > potential of slowing down DRV may not be a good thing in a refactoring
> > series.
> >   
> 
> Note, that currently it's "only" the XDP_SKB path that's affected, but
> yeah, I agree with out. And going forward, I'd like to use the netdev
> xdp_prog from the Intel drivers, instead of spreading/caching it all over.
> 
> I'll go back to the drawing board. Any suggestions on a how/where the
> program should be stored in the netdev are welcome! :-) ...or maybe just
> simply store the netdev_xdp flat (w/o the additional allocation step) in
> net_device. Three programs and the boolean (remove the num_progs).

Three progs?  Are we planning to allow SKB and DRV at the same time?
One prog and flags looked fairly reasonable to me.  Flags can even be
a u8.  The offload prog can continue to live in the driver.