Re: [PATCH net] veth: Fix RX stats for bpf_redirect_peer() traffic

[Daniel Borkmann]

On 10/31/23 8:53 PM, Jakub Kicinski wrote:
> On Mon, 30 Oct 2023 15:19:26 +0100 Daniel Borkmann wrote:
> > > Since I didn't want to update host-veth's TX counters.  If we
> > > bpf_redirect_peer()ed a packet from NIC TC ingress to Pod-veth TC ingress,
> > > I think it means we've bypassed host-veth TX?
> >
> > Yes. So the idea is to transition to tstats replace the location where
> > we used to bump lstats with tstat's tx counter, and only the peer redirect
> > would bump the rx counter.. then upon stats traversal we fold the latter into
> > the rx stats which was populated by the opposite's tx counters. Makes sense.
> >
> > OT: does cadvisor run inside the Pod to collect the device stats? Just
> > curious how it gathers them.
>
> Somewhat related - where does netkit count stats?

Yeap, it needs it as well, I have a local branch here where I pushed all
of it - coming out soon; I was planning to add some selftests in addition
till end of this week:

https://github.com/cilium/linux/commits/pr/ndo_peer

> > > > Definitely no new stats ndo resp indirect call in fast path.
> > >
> > > Yeah, I think I'll put a comment saying that all devices that support
> > > BPF_F_PEER must use tstats (or must use lstats), then.
> >
> > sgtm.
>
> Is comment good enough? Can we try to do something more robust?
> Move the allocation of stats into the core at registration based
> on some u8 assigned in the driver? (I haven't looked at the code TBH)
Hm, not sure. One thing that comes to mind is lazy one-time allocation
like in case of netdev_core_stats_inc(), so whenever one of the helpers
like dev_sw_netstats_{rx,tx}_add() are called and dev->tstats are still
NULL, the core knows about the driver's intent, but tbh that doesn't
feel overly clean and in case of netdev_core_stats_inc() it's more in
the exception case rather than fast-path.

Other option could be to have two small helpers in the core which then
set a flag as well:

static inline int netdev_tstats_alloc(struct net_device *dev)
{
	dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
	if (!dev->tstats)
		return -ENOMEM;
	dev->priv_flags |= IFF_USES_TSTATS;
	return 0;
}

static inline void netdev_tstats_free(struct net_device *dev)
{
	free_percpu(dev->tstats);
}

They can then be used from .ndo_init/uninit - not sure if this would
be overall nicer.. or just leaving it at the .ndo callback comment for
the time being until really more users show up (which I doubt tbh).

Thanks,
Daniel