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

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Date:   Wed, 4 Aug 2021 18:43:19 -0600
From:   David Ahern <dsahern@...il.com>
To:     Saeed Mahameed <saeed@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Tariq Toukan <ttoukan.linux@...il.com>,
        Tariq Toukan <tariqt@...dia.com>
Cc:     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 8/4/21 12:27 PM, Saeed Mahameed wrote:
> 
>> I just ran some quick tests with my setup and measured about 1.2%
>> worst
> 
> 1.2% is a lot ! what was the test ? what is the change ?

I did say "quick test ... not exhaustive" and it was definitely
eyeballing a pps change over a small time window.

If multiple counters are bumped 20-25 million times a second (e.g. XDP
drop case), how measurable is it? I was just trying to ballpark the
overhead - 1%, 5%, more? If it is <~ 1% then there is no performance
argument in which case let's do the right thing for users - export via
existing APIs.