Re: [PATCH v2 net-next 21/26] ice: add XDP and XSK generic per-channel statistics

[Jakub Kicinski]

On Sun, 28 Nov 2021 19:54:53 +0200 Ido Schimmel wrote:
> > > Right, sure, I am also totally fine with having only a somewhat
> > > restricted subset of stats available at the interface level and make
> > > everything else be BPF-based. I'm hoping we can converge of a common
> > > understanding of what this "minimal set" should be :)
> > > 
> > > Agreed. My immediate thought is that "XDP packets are interface packets"
> > > but that is certainly not what we do today, so not sure if changing it
> > > at this point would break things?  
> > 
> > I'd vote for taking the risk and trying to align all the drivers.  
> 
> I agree. I think IFLA_STATS64 in RTM_NEWLINK should contain statistics
> of all the packets seen by the netdev. The breakdown into software /
> hardware / XDP should be reported via RTM_NEWSTATS.

Hm, in the offload case "seen by the netdev" may be unclear. For 
the offload case I believe our recommendation was phrased more like 
"all packets which would be seen by the netdev if there was no
routing/tc offload", right?

> Currently, for soft devices such as VLANs, bridges and GRE, user space
> only sees statistics of packets forwarded by software, which is quite
> useless when forwarding is offloaded from the kernel to hardware.
> 
> Petr is working on exposing hardware statistics for such devices via
> rtnetlink. Unlike XDP (?), we need to be able to let user space enable /
> disable hardware statistics as we have a limited number of hardware
> counters and they can also reduce the bandwidth when enabled. We are
> thinking of adding a new RTM_SETSTATS for that:
> 
> # ip stats set dev swp1 hw_stats on

Does it belong on the switch port? Not the netdev we want to track?

> For query, something like (under discussion):
> 
> # ip stats show dev swp1 // all groups
> # ip stats show dev swp1 group link
> # ip stats show dev swp1 group offload // all sub-groups
> # ip stats show dev swp1 group offload sub-group cpu
> # ip stats show dev swp1 group offload sub-group hw
> 
> Like other iproute2 commands, these follow the nesting of the
> RTM_{NEW,GET}STATS uAPI.

But we do have IFLA_STATS_LINK_OFFLOAD_XSTATS, isn't it effectively 
the same use case?

> Looking at patch #1 [1], I think that whatever you decide to expose for
> XDP can be queried via:
> 
> # ip stats show dev swp1 group xdp
> # ip stats show dev swp1 group xdp sub-group regular
> # ip stats show dev swp1 group xdp sub-group xsk
> 
> Regardless, the following command should show statistics of all the
> packets seen by the netdev:
> 
> # ip -s link show dev swp1
> 
> There is a PR [2] for node_exporter to use rtnetlink to fetch netdev
> statistics instead of the old proc interface. It should be possible to
> extend it to use RTM_*STATS for more fine-grained statistics.
> 
> [1] https://lore.kernel.org/netdev/20211123163955.154512-2-alexandr.lobakin@xxxxxxxxx/
> [2] https://github.com/prometheus/node_exporter/pull/2074

Nice!