netdev - Re: [RFC PATCH net-next 2/4] net: dsa: remove the "dsa_to_port in a loop" antipattern from the core

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Date:   Tue, 10 Aug 2021 02:41:07 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     DENG Qingfang <dqfext@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        George McCollister <george.mccollister@...il.com>
Subject: Re: [RFC PATCH net-next 2/4] net: dsa: remove the "dsa_to_port in a
 loop" antipattern from the core



On 8/9/2021 8:33 PM, DENG Qingfang wrote:
> On Mon, Aug 09, 2021 at 10:03:18PM +0300, Vladimir Oltean wrote:
>> Ever since Vivien's conversion of the ds->ports array into a dst->ports
>> list, and the introduction of dsa_to_port, iterations through the ports
>> of a switch became quadratic whenever dsa_to_port was needed.
> 
> So, what is the benefit of a linked list here? Do we allow users to
> insert/delete a dsa_port at runtime? If not, how about using a
> dynamically allocated array instead?

The goal was to flatten the space while doing cross switch operations, 
which would have otherwise required iterating over dsa_switch instances 
within a dsa_switch_tree, and then over dsa_port within each dsa_switch.
-- 
Florian