From: "Russell King (Oracle)" <linux@armlinux•org.uk>
To: arinc9.unal@gmail•com
Cc: "Arınç ÜNAL" <arinc.unal@arinc9•com>,
"Daniel Golle" <daniel@makrotopia•org>,
"Landen Chao" <Landen.Chao@mediatek•com>,
"DENG Qingfang" <dqfext@gmail•com>,
"Sean Wang" <sean.wang@mediatek•com>,
"Andrew Lunn" <andrew@lunn•ch>,
"Florian Fainelli" <f.fainelli@gmail•com>,
"Vladimir Oltean" <olteanv@gmail•com>,
"David S. Miller" <davem@davemloft•net>,
"Eric Dumazet" <edumazet@google•com>,
"Jakub Kicinski" <kuba@kernel•org>,
"Paolo Abeni" <pabeni@redhat•com>,
"Matthias Brugger" <matthias.bgg@gmail•com>,
"AngeloGioacchino Del Regno"
<angelogioacchino.delregno@collabora•com>,
"Frank Wunderlich" <frank-w@public-files•de>,
"Bartel Eerdekens" <bartel.eerdekens@constell8•be>,
mithat.guner@xeront•com, erkin.bozoglu@xeront•com,
linux-kernel@vger•kernel.org, netdev@vger•kernel.org,
linux-arm-kernel@lists•infradead.org,
linux-mediatek@lists•infradead.org
Subject: Re: [PATCH net v6 5/6] net: dsa: introduce preferred_default_local_cpu_port and use on MT7530
Date: Mon, 19 Jun 2023 13:14:02 +0100 [thread overview]
Message-ID: <ZJBGij0SUZr644w5@shell.armlinux.org.uk> (raw)
In-Reply-To: <20230617062649.28444-6-arinc.unal@arinc9.com>
On Sat, Jun 17, 2023 at 09:26:48AM +0300, arinc9.unal@gmail•com wrote:
> From: Vladimir Oltean <olteanv@gmail•com>
>
> Since the introduction of the OF bindings, DSA has always had a policy that
> in case multiple CPU ports are present in the device tree, the numerically
> smallest one is always chosen.
>
> The MT7530 switch family, except the switch on the MT7988 SoC, has 2 CPU
> ports, 5 and 6, where port 6 is preferable on the MT7531BE switch because
> it has higher bandwidth.
>
> The MT7530 driver developers had 3 options:
> - to modify DSA when the MT7531 switch support was introduced, such as to
> prefer the better port
> - to declare both CPU ports in device trees as CPU ports, and live with the
> sub-optimal performance resulting from not preferring the better port
> - to declare just port 6 in the device tree as a CPU port
>
> Of course they chose the path of least resistance (3rd option), kicking the
> can down the road. The hardware description in the device tree is supposed
> to be stable - developers are not supposed to adopt the strategy of
> piecemeal hardware description, where the device tree is updated in
> lockstep with the features that the kernel currently supports.
>
> Now, as a result of the fact that they did that, any attempts to modify the
> device tree and describe both CPU ports as CPU ports would make DSA change
> its default selection from port 6 to 5, effectively resulting in a
> performance degradation visible to users with the MT7531BE switch as can be
> seen below.
>
> Without preferring port 6:
>
> [ ID][Role] Interval Transfer Bitrate Retr
> [ 5][TX-C] 0.00-20.00 sec 374 MBytes 157 Mbits/sec 734 sender
> [ 5][TX-C] 0.00-20.00 sec 373 MBytes 156 Mbits/sec receiver
> [ 7][RX-C] 0.00-20.00 sec 1.81 GBytes 778 Mbits/sec 0 sender
> [ 7][RX-C] 0.00-20.00 sec 1.81 GBytes 777 Mbits/sec receiver
>
> With preferring port 6:
>
> [ ID][Role] Interval Transfer Bitrate Retr
> [ 5][TX-C] 0.00-20.00 sec 1.99 GBytes 856 Mbits/sec 273 sender
> [ 5][TX-C] 0.00-20.00 sec 1.99 GBytes 855 Mbits/sec receiver
> [ 7][RX-C] 0.00-20.00 sec 1.72 GBytes 737 Mbits/sec 15 sender
> [ 7][RX-C] 0.00-20.00 sec 1.71 GBytes 736 Mbits/sec receiver
>
> Using one port for WAN and the other ports for LAN is a very popular use
> case which is what this test emulates.
>
> As such, this change proposes that we retroactively modify stable kernels
> (which don't support the modification of the CPU port assignments, so as to
> let user space fix the problem and restore the throughput) to keep the
> mt7530 driver preferring port 6 even with device trees where the hardware
> is more fully described.
>
> Fixes: c288575f7810 ("net: dsa: mt7530: Add the support of MT7531 switch")
> Signed-off-by: Vladimir Oltean <olteanv@gmail•com>
> Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9•com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux•org.uk>
Thanks!
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
next prev parent reply other threads:[~2023-06-19 12:14 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-17 6:26 [PATCH net v6 0/6] net: dsa: mt7530: fix multiple CPU ports, BPDU and LLDP handling arinc9.unal
2023-06-17 6:26 ` [PATCH net v6 1/6] net: dsa: mt7530: set all CPU ports in MT7531_CPU_PMAP arinc9.unal
2023-06-19 16:01 ` Florian Fainelli
2023-06-17 6:26 ` [PATCH net v6 2/6] net: dsa: mt7530: fix trapping frames on non-MT7621 SoC MT7530 switch arinc9.unal
2023-06-19 12:11 ` Russell King (Oracle)
2023-06-19 16:02 ` Florian Fainelli
2023-06-17 6:26 ` [PATCH net v6 3/6] net: dsa: mt7530: fix handling of BPDUs on " arinc9.unal
2023-06-19 11:55 ` Vladimir Oltean
2023-06-19 12:12 ` Russell King (Oracle)
2023-06-19 16:03 ` Florian Fainelli
2023-06-17 6:26 ` [PATCH net v6 4/6] net: dsa: mt7530: fix handling of LLDP frames arinc9.unal
2023-06-19 11:56 ` Vladimir Oltean
2023-06-19 12:13 ` Russell King (Oracle)
2023-06-19 16:04 ` Florian Fainelli
2023-06-17 6:26 ` [PATCH net v6 5/6] net: dsa: introduce preferred_default_local_cpu_port and use on MT7530 arinc9.unal
2023-06-19 12:14 ` Russell King (Oracle) [this message]
2023-06-19 16:05 ` Florian Fainelli
2023-06-17 6:26 ` [PATCH net v6 6/6] MAINTAINERS: add me as maintainer of MEDIATEK SWITCH DRIVER arinc9.unal
2023-06-19 15:10 ` Matthias Brugger
2023-06-19 15:11 ` Matthias Brugger
2023-06-19 16:05 ` Florian Fainelli
2023-06-20 12:40 ` [PATCH net v6 0/6] net: dsa: mt7530: fix multiple CPU ports, BPDU and LLDP handling patchwork-bot+netdevbpf
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