linux-kernel - Re: [PATCH net-next 03/21] ethtool, stats: introduce standard XDP statistics

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Date:   Thu, 12 Aug 2021 14:19:30 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>, David Ahern <dsahern@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>
Cc:     brouer@...hat.com, Saeed Mahameed <saeed@...nel.org>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Lukasz Czapnik <lukasz.czapnik@...el.com>,
        Marcin Kubiak <marcin.kubiak@...el.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        Michal Swiatkowski <michal.swiatkowski@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Netanel Belgazal <netanel@...zon.com>,
        Arthur Kiyanovski <akiyano@...zon.com>,
        Guy Tzalik <gtzalik@...zon.com>,
        Saeed Bishara <saeedb@...zon.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Shay Agroskin <shayagr@...zon.com>,
        Sameeh Jubran <sameehj@...zon.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Danielle Ratson <danieller@...dia.com>,
        Ido Schimmel <idosch@...dia.com>, Andrew Lunn <andrew@...n.ch>,
        Vladyslav Tarasiuk <vladyslavt@...dia.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jian Shen <shenjian15@...wei.com>,
        Petr Vorel <petr.vorel@...il.com>, Dan Murphy <dmurphy@...com>,
        Yangbo Lu <yangbo.lu@....com>,
        Michal Kubecek <mkubecek@...e.cz>,
        Zheng Yongjun <zhengyongjun3@...wei.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Johannes Berg <johannes@...solutions.net>,
        netdev@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next 03/21] ethtool, stats: introduce standard XDP
 statistics


On 04/08/2021 18.44, Jakub Kicinski wrote:
> On Wed, 4 Aug 2021 10:17:56 -0600 David Ahern wrote:
>> On 8/4/21 6:36 AM, Jakub Kicinski wrote:
> 
>> Does anyone have data that shows bumping a properly implemented counter
>> causes a noticeable performance degradation and if so by how much? You
>> mention 'yet another cacheline' but collecting stats on stack and
>> incrementing the driver structs at the end of the napi loop should not
>> have a huge impact versus the value the stats provide.
> 
> Not sure, maybe Jesper has some numbers. Maybe Intel folks do?

(sorry, behind on emails after vacation ... just partly answering inside 
this thread, not checking if you did a smart counter impl.).

I don't have exact numbers, but I hope Magnus (Intel) would be motivated 
to validate performance degradation from this patchset.  As I know Intel 
is hunting the DPDK numbers with AF_XDP-zc, where every last cycle *do* 
count.

My experience is that counters can easily hurt performance, without the 
developers noticing the small degradation's.  As Ahern sketch out above 
(stats on stack + end of napi loop update), I do believe that a smart 
counter implementation is possible to hide this overhead (hopefully 
completely in the CPUs pipeline slots).

I do highly appreciate the effort to standardize the XDP stats!
So, I do hope this can somehow move forward.

--Jesper