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

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Date:   Tue, 30 Nov 2021 12:55:47 +0100
From:   Petr Machata <petrm@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Petr Machata <petrm@...dia.com>, Ido Schimmel <idosch@...sch.org>,
        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>, <nikolay@...dia.com>
Subject: Re: [PATCH v2 net-next 21/26] ice: add XDP and XSK generic
 per-channel statistics


Jakub Kicinski <kuba@...nel.org> writes:

> On Mon, 29 Nov 2021 18:08:12 +0100 Petr Machata wrote:
>> For those who care to know about the offloaded datapath, it would be
>> nice to have the option to request either just the SW stats, or just the
>> HW stats. A logical place to put these would be under the OFFLOAD_XSTATS
>> nest of the RTM_GETSTATS message, but maybe the SW ones should be up
>> there next to IFLA_STATS_LINK_64. (After all it's going to be
>> independent from not only offload datapath, but also XDP.)
>
> What I'm getting at is that I thought IFLA_OFFLOAD_XSTATS_CPU_HIT
> should be sufficient from uAPI perspective in terms of reporting.
> User space can do the simple math to calculate the "SW stats" if 
> it wants to. We may well be talking about the same thing, so maybe
> let's wait for the code?

Ha, OK, now I understand. Yeah, CPU_HIT actually does fit the bill for
the traffic that took place in SW. We can reuse it.

I still think it would be better to report HW_STATS explicitly as well
though. One reason is simply convenience. The other is that OK, now we
have SW stats, and XDP stats, and total stats, and I (as a client) don't
necessarily know how it all fits together. But the contract for HW_STATS
is very clear.