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

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Message-ID: <20211129064755.539099c0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 29 Nov 2021 06:47:55 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Shay Agroskin <shayagr@...zon.com>,
        Arthur Kiyanovski <akiyano@...zon.com>,
        David Arinzon <darinzon@...zon.com>,
        Noam Dagan <ndagan@...zon.com>,
        Saeed Bishara <saeedb@...zon.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Yajun Deng <yajun.deng@...ux.dev>,
        Sergey Ryazanov <ryazanov.s.a@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Cong Wang <cong.wang@...edance.com>, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, petrm@...dia.com,
        nikolay@...dia.com
Subject: Re: [PATCH v2 net-next 21/26] ice: add XDP and XSK generic
 per-channel statistics

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@intel.com/
> [2] https://github.com/prometheus/node_exporter/pull/2074

Nice!