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Vladimir Oltean d9c2f69cc1 net: dsa: introduce preferred_default_local_cpu_port and use on MT7530 
commit b79d7c14f4 upstream.

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: c288575f78 ("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>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-04-27 17:07:17 +02:00
arch arm64: hibernate: Fix level3 translation fault in swsusp_save() 2024-04-27 17:07:16 +02:00
block block: prevent division by zero in blk_rq_stat_sum() 2024-04-13 13:05:12 +02:00
certs
crypto crypto: jitter - fix CRYPTO_JITTERENTROPY help text 2024-03-26 18:20:50 -04:00
Documentation usb: new quirk to reduce the SET_ADDRESS request timeout 2024-04-27 17:07:12 +02:00
drivers net: dsa: introduce preferred_default_local_cpu_port and use on MT7530 2024-04-27 17:07:17 +02:00
fs nilfs2: fix OOB in nilfs_set_de_type 2024-04-27 17:07:17 +02:00
include net: dsa: introduce preferred_default_local_cpu_port and use on MT7530 2024-04-27 17:07:17 +02:00
init init/main.c: Fix potential static_command_line memory overflow 2024-04-27 17:07:16 +02:00
io_uring io_uring: Fix io_cqring_wait() not restoring sigmask on get_timespec64() failure 2024-04-27 17:07:04 +02:00
ipc
kernel x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n 2024-04-17 11:18:27 +02:00
lib bootconfig: use memblock_free_late to free xbc memory to buddy 2024-04-27 17:07:17 +02:00
LICENSES
mm mm/memory-failure: fix deadlock when hugetlb_optimize_vmemmap is enabled 2024-04-27 17:07:16 +02:00
net net: dsa: introduce preferred_default_local_cpu_port and use on MT7530 2024-04-27 17:07:17 +02:00
rust
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:12:28 +01:00
scripts gcc-plugins/stackleak: Avoid .head.text section 2024-04-13 13:05:23 +02:00
security landlock: Warn once if a Landlock action is requested while disabled 2024-04-03 15:19:32 +02:00
sound ALSA: hda/realtek - Enable audio jacks of Haier Boyue G42 with ALC269VC 2024-04-27 17:07:13 +02:00
tools selftests/ftrace: Limit length in subsystem-enable tests 2024-04-27 17:07:04 +02:00
usr
virt KVM: Always flush async #PF workqueue when vCPU is being destroyed 2024-04-03 15:19:25 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
.rustfmt.toml
COPYING
CREDITS
Kbuild
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MAINTAINERS ALSA: scarlett2: Rename scarlett_gen2 to scarlett2 2024-04-27 17:07:11 +02:00
Makefile Linux 6.1.87 2024-04-17 11:18:29 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
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Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.