Reduced throughput with mt7621 and DSA

[Kristian Evensen]

Hello again,

On Sun, Dec 19, 2021 at 12:29 PM Kristian Evensen
<kristian.evensen at gmail.com> wrote:
> Based on my measurements, the throughput is reduced by ~50% going from
> 19.07 and to 21.02/master (~450Mbit/s vs. ~900Mbit/s). I do not have a
> particular commit I can point to, but I believe the regressions is
> caused by the introduction of DSA. Restoring the old swconfig driver,
> brings my 21.02/master throughput up to roughly the same level as
> 19.07.

I kept working on this issue today and went through my previous setup
and results. It turns out that I had mixed my 21.02 and master
results, leading to an incorrect observation. After cleaning up my
mess and repeating my tests, I get roughly the same result for master
(with DSA) as with 19.07.8. With an adequate number of parallel
connections (eight seems to be a good number), I am able to reach
900Mbit/s-1Gbit/s. 21.02.1 peaks at around 500 Mbit/s.

Since the only change between my sets of tests is the software,
something has clearly improved in either the kernel or OpenWrt (as
would be expected :)). Are there any particular commits/patches that
would be worthwhile trying to backport to 21.02/5.4, or is the
difference to master/5.10 so big that there is no point and the best
is to wait for the next release? I guess one thing that hopefully
shouldn't be too hard is be to combine 21.02 userspace with the 5.10
kernel. That will be on the top of my todo-list for tomorrow.

Kristian