Wrt1900acs v2 poor performance on the ethernet side

Hello all,
I use the following router configuration with the following firmware :

 System OpenWrt|
Model|Linksys WRT1900ACS v2
|Architecture|ARMv7 Processor rev 1 (v7l)|
|Firmware Version|OpenWrt 21.02-SNAPSHOT r16267-94efa1c612 / LuCI openwrt-21.02 branch git-21.188.55099-e52e1de|
|Kernel Version|5.4.137|

Since last year, when openwrt implemented and adopted DSA, this router on the ethernet side does not exceed 890Mbps!
Currently my provider provides me 1Gbps internet, PPPoE IPv4 / IPv6 dual-stack connection, I encounter this problem only on versions starting with OpenWrt 21.02.0 , on previous versions 19.07 everything moves well in the speed test 940Mbps.
I use the same standard packages from https://chef.libremesh.org/ when customizing the image!

You know this problem will be solved in time ?

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In time, no - but hopefully it will be.

Mainline DSA has no concept of multiple CPU ports yet, several patches have been proposed, none have been accepted by the netdev maintainers so far. Accordingly targets which have switched to DSA can only use a single CPU port so far, while the hardware supports two (and would need both of them, to cover forwarding at 1 symmetric GBit/s wirespeed; as you noticed, in practice the impact isn't quite as bad as implied on paper).

Among other things, https://github.com/openwrt/openwrt/pull/4036 tries to add support for multiple CPU ports again (to get it working on your device would require some changes in the mvebu target as well), but that's certainly not going to be added to openwrt-21.02 anymore.

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