linux-kernel - RE: [PATCH] r8169: introduce polling method for link change

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Date:   Mon, 7 Jun 2021 12:32:29 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Koba Ko' <koba.ko@...onical.com>,
        Heiner Kallweit <hkallweit1@...il.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] r8169: introduce polling method for link change

From: Koba Ko
> Sent: 07 June 2021 05:35
...
> After consulting with REALTEK, I can identify RTL8106e by PCI_VENDOR
> REALTEK, DEVICE 0x8136, Revision 0x7.
> I would like to make PHY_POLL as default for RTL8106E on V2.
> because there's no side effects besides the cpu usage rate would be a
> little higher,
> How do you think?

If reading the PHY registers involves a software bit-bang
of an MII register (rather than, say, a sleep for interrupt
while the MAC unit does the bit-bang) then you can clobber
interrupt latency because of all the time spent spinning.

While this is less of a problem on multi-cpu systems I have
seen it result in ethernet packet loss on old systems.

	David

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