OK, recovery was easier than I expected (opening the device and connecting the UART was the "hard" part, the rest was easy).
After I successfully recovered the device, I wanted to be sure the issue was not with my build. So I downloaded today's snapshot image from OpenWRT website and the results are the same as above. So be aware Archer C6 v3 users (as well as A6 v3) that as of January 30rd 2022 the snapshot builds will brick your device (and a UART connection will be required to recover it).
Lol (?) ...
Ok maybe I'll wait for next snapshot. I'm flashing a snapshot 2 or 3 times a week for the mt7621 and it has always worked. I know that snapshot are not garantied to work, for so far I had no real issue. Today's snapshot is still based on 5.10.92. I'll wait for the next based on 5.10.95.
Notice that this issue might affect only my device (Archer C6 v3 and A6 v3) and not all mt7621 devices.
So even with kernel 5.10.92 which is problematic in my experience you may have better luck with a different device.
BTW, due to a complete lack of error messages I am assuming the kernel is the issue (since it hung while loading), but it might be something else in this build.
Please continue the debate here (and maybe help by trying the possible fix) as this problem is not related to SW/HW offload (which is the topic of this thread):
I just tested a new snapshot build today (r18710-dc2da6a233, kernel 5.10.96). Things got worse:
With the now default firewall4, enabling HW flow offload breaks the firewall and all connected devices lose internet connectivity. Basically firewall4 is not able to recognize the flag option flow_offloading_hw '1' in the firewall config file. More details here.
Redoing the build but selecting firewall3 instead, enabling HW flow offload now has no effect. I've monitored the CPU usage (medium/high) during a heavy download, and even with HW flow offload enabled the CPU usage is the same as disabled. With firewall3 and kernel 5.4 HW flow offload works perfectly and the CPU usage is minimum.
Once again rolled back to snapshot r18324-794e8123ce (kernel 5.4.162), the last snapshot build that has HW offload working and stable.
Just tried on a R6220 with Feb3 OpenWrt SNAPSHOT r18717-0e32c6baf3 (kernel 5.10.96)
Firewall is firewall4 (nftables).
basic settings : 610 Mbit/s
SW offloading : 630 Mbits/s
SW/HW Offloading : 600 Mbit/s
All results are very close and offloading doesn't seem to be active.
When I click on status/firewall I have no answer, and apparently no firewall process in system/processes.
BTW I have a symetric 1Gbit/s fiber which I normally use with a x86 router.
Are you sure that you followed the thread ?
HW offloading is implemented in mt7621. It was working with previous kernels (even early 5.10), so there is a regression in the actual code. I'm just testing from time to time in order to help @dsouza by comparing with another device than his.
My main router is an x86/64. I have this precisely for its CPU power and no offloading
Besides moving kernel from 5.4 to 5.10, the current snapshot builds also moved from firewall3 (iptables) to firewall4 (nftables).
HW offload for mt7621 is implemented only in iptables. But iptables with hardware acceleration has compatibility issues with Kernel 5.10 (current kernel version in snapshot, original post of this thread).
Bottom line is that mt7621 HW offload is currently broken in the snapshot builds with no solution in foreseeable future. Even doing a build with Kernel 5.10 and iptables, HW offload does not seem to work anymore.
For this reason I am using the last snapshot build with kernel 5.4 and iptables. With this configuration HW offload is running rock solid on an Archer C6 v3.2.
@Vladdrako, are you using an mt7621 device with HW offload enabled?
If so, have you verified CPU usage? I did this last weekend, enabling HW offload in the latest builds had no effect (CPU usage remained high even when HW offload was enabled).
So while enabling HW offload with nftables does not break it anymore, in fact it is not working.
As you can see in the commit below, HW offload has been disabled in the current firewall4/nftables therefore enabling it has no effect:
Currently there does not appear to exist any kernel side nft flowtable
implementation that supports hardware flow offloading.
Attempting to upload a ruleset containing a flowtable declaration with
the hardware offloading flag set will fail with a generic EOPNOTSUPP
error.
Since there is neither a graceful recovery (e.g. continue without
hardware flow offloading) nor any possibility to probe kernel side
support from userspace, disable the facility entirely for now.
Sorry I can't reply : I only setup the router a few minutes in order to check how it works, and perform bandwith tests. It is running as an AP right now. I'll perform another tests with the next kernel release.