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From: DENG Qingfang <dqfext@gmail.com>
To: netdev <netdev@vger.kernel.org>, Andrew Lunn <andrew@lunn.ch>,
	Jakub Kicinski <kuba@kernel.org>,
	David Miller <davem@davemloft.net>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	linux-kernel@vger.kernel.org,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: "Birger Koblitz" <git@birger-koblitz.de>,
	"Bjørn Mork" <bjorn@mork.no>,
	"Stijn Segers" <foss@volatilesystems.org>
Subject: dsa_master_find_slave()'s time complexity and potential performance hit
Date: Tue, 2 Mar 2021 13:51:42 +0800	[thread overview]
Message-ID: <CALW65jatBuoE=NDRqccfiMVugPh5eeYSf-9a9qWYhvvszD2Jiw@mail.gmail.com> (raw)

Since commit 7b9a2f4bac68 ("net: dsa: use ports list to find slave"),
dsa_master_find_slave() has been iterating over a linked list instead
of accessing arrays, making its time complexity O(n).
The said function is called frequently in DSA RX path, so it may cause
a performance hit, especially for switches that have many ports (20+)
such as RTL8380/8390/9300 (There is a downstream DSA driver for it,
see https://github.com/openwrt/openwrt/tree/openwrt-21.02/target/linux/realtek/files-5.4/drivers/net/dsa/rtl83xx).
I don't have one of those switches, so I can't test if the performance
impact is huge or not.

             reply	other threads:[~2021-03-02  8:24 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-02  5:51 DENG Qingfang [this message]
2021-03-02 11:28 ` dsa_master_find_slave()'s time complexity and potential performance hit Vladimir Oltean

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