TP-Link Archer C6U mt7615 interrupts problem

Hello!

I have some problems with an Archer C6U v1 router.
It's based on MediaTek MT7621 SoC, and a MT7603 2.4 GHz and MT7613 5 GHz wireless PCIe adapters.

The first problem is the massive interrupt errors, that caused by the MT7615 wlan adapter.
(shown on pic.)
After 2 days of uptime, the problem is appears and the ksoftirqd on 3th CPU hangs on 25% of usage.
I'm tryied to complete disabling both 2.4 and 5 G wireless. This solved the problem, but after 5 days of uptime the problem is present again.

I'm tryed different version of OpenWrt 21.02 from 21.02.0-rc3 to 21.02.1, but nothing changes.

The second problem is the IPv6 and flow offload. I'm read from this on forum. When offload and IPv6 (I have native IPv6 from my ISP) enabled, the pages f.ex. google, facebook etc. loads slowly and some picture not loaded.
For a solution, I deleting the IPv6 ULA prefix. That helps a bit, but not the best.

There are any solution to this problems?

You can try to flash latest snapshot. I have no troubles with ksoftirqd for a long time.

I'm installed the r18785-8072bf3322 snapshot, released on feb 10. and it's running more than 2 days without the ksoftirqd problem.
The interrupt errors still remaining, and the number of ERR: in /proc/interrupts increasing fastly when I intensively use the 5G wifi, f.ex. downloading something or make a speedtest, but I'm not experienced another problems. I will be testing it for a longer time.

Linux OpenWrt 5.10.96 #0 SMP Thu Feb 10 20:08:09 2022 mips GNU/Linux
 15:26:51 up 2 days, 20:39,  load average: 0.03, 0.02, 0.00
           CPU0       CPU1       CPU2       CPU3
  7:          0          0          0          0      MIPS   7  timer
  8:   24713007   24712991   24712983   24712975  MIPS GIC Local   1  timer
  9:   26496744          0          0          0  MIPS GIC  63  IPI call
 10:          0   47822497          0          0  MIPS GIC  64  IPI call
 11:          0          0   38775957          0  MIPS GIC  65  IPI call
 12:          0          0          0   50036875  MIPS GIC  66  IPI call
 13:     948027          0          0          0  MIPS GIC  67  IPI resched
 14:          0     564422          0          0  MIPS GIC  68  IPI resched
 15:          0          0   11763621          0  MIPS GIC  69  IPI resched
 16:          0          0          0   14061731  MIPS GIC  70  IPI resched
 17:          0          0          0          0  MIPS GIC  19  1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
 19:         12          0          0          0  MIPS GIC  33  ttyS0
 20:          0          0          0          0  MIPS GIC  29  xhci-hcd:usb1
 21:    6520591          0          0          0  MIPS GIC  10  1e100000.ethernet
 22:         23          0   23828554          0  MIPS GIC  11  mt7603e
 23:         16          0          0    8981249  MIPS GIC  31  mt7615e
 25:         29          0          0          0  MIPS GIC  30  mt7530
 26:          1          0          0          0    mt7530   0  mt7530-0:00
 27:         23          0          0          0    mt7530   1  mt7530-0:01
 28:          5          0          0          0    mt7530   2  mt7530-0:02
 29:          0          0          0          0    mt7530   3  mt7530-0:03
 30:          0          0          0          0    mt7530   4  mt7530-0:04
 31:          0          0          0          0  1e000600.gpio   8  keys
 32:          0          0          0          0  1e000600.gpio  10  keys
ERR:      11751

I can confirm the ksoftirqd/3 cpu load behavior. I have 3 of the same routers on the stable release, strangely enough, I don't see it on the other 2. Both are online much longer than the 3rd one.

root@caretaker3:~# uptime
 13:09:25 up  1:38,  load average: 1.61, 1.65, 1.67

root@caretaker2:~# uptime
 15:55:55 up 14:58,  load average: 0.00, 0.00, 0.00

root@caretaker1:~# uptime
 13:09:52 up 14:58,  load average: 0.06, 0.03, 0.00

All are running:

OpenWrt 21.02.1, r16325-88151b8303

caretaker1 -> main router (WDS master)
caretaker2 -> WDS client
caretaker3 -> recently installed, WIFI cards are disabled , just connected on caretaker2 with LAN cable

Only caretaker1 is connected using WAN interface here.

root@caretaker3:~# cat /proc/interrupts 
           CPU0       CPU1       CPU2       CPU3       
  8:    1583542    1583518    1583430    1583485  MIPS GIC Local   1  timer
  9:     384848          0          0          0  MIPS GIC  63  IPI call
 10:          0      21999          0          0  MIPS GIC  64  IPI call
 11:          0          0     684494          0  MIPS GIC  65  IPI call
 12:          0          0          0      17403  MIPS GIC  66  IPI call
 13:  153206524          0          0          0  MIPS GIC  67  IPI resched
 14:          0  160359768          0          0  MIPS GIC  68  IPI resched
 15:          0          0    5045583          0  MIPS GIC  69  IPI resched
 16:          0          0          0      32542  MIPS GIC  70  IPI resched
 17:          0          0          0          0  MIPS GIC  19  1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
 19:         12          0          0          0  MIPS GIC  33  ttyS0
 20:          0          0          0          0  MIPS GIC  29  xhci-hcd:usb1
 21:      18710          0          0          0  MIPS GIC  10  1e100000.ethernet
 23:         23          0          0          0  MIPS GIC  11  mt7603e
 24:         16          0          0  327156842  MIPS GIC  31  mt7615e
 26:          0          0          0          0  1e000600.gpio   8  keys
 27:          0          0          0          0  1e000600.gpio  10  keys
ERR:       5371

I re-checked and both radio's are disabled on this router.

The router that is doing the most the ERR counter is not rising:

root@caretaker1:~# cat /proc/interrupts 
           CPU0       CPU1       CPU2       CPU3       
  8:   13611287   13611013   13610515   13611387  MIPS GIC Local   1  timer
  9:     982356          0          0          0  MIPS GIC  63  IPI call
 10:          0      43540          0          0  MIPS GIC  64  IPI call
 11:          0          0     854987          0  MIPS GIC  65  IPI call
 12:          0          0          0      78003  MIPS GIC  66  IPI call
 13:    1152587          0          0          0  MIPS GIC  67  IPI resched
 14:          0    1176937          0          0  MIPS GIC  68  IPI resched
 15:          0          0     933843          0  MIPS GIC  69  IPI resched
 16:          0          0          0     579682  MIPS GIC  70  IPI resched
 17:          0          0          0          0  MIPS GIC  19  1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
 19:         12          0          0          0  MIPS GIC  33  ttyS0
 20:          0          0          0          0  MIPS GIC  29  xhci-hcd:usb1
 21:     180854          0          0          0  MIPS GIC  10  1e100000.ethernet
 23:         22          0          0          0  MIPS GIC  11  mt7603e
 24:         18          0          0    1731029  MIPS GIC  31  mt7615e
 26:          0          0          0          0  1e000600.gpio   8  keys
 27:          0          0          0          0  1e000600.gpio  10  keys
ERR:         72

I'm updated the router with the secod service release of 21.02 (OpenWrt 21.02.2).
I'm tested it over up to 16 days with normal usage. The errors in /proc/interrupts still increased, but the ksoftirqd CPU issue not appeared, so it seems to be fixed in this release.

root@Archer_C6U:~# cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3
  8:  345593988  345593998  345594032  345594019  MIPS GIC Local   1  timer
  9:     533744          0          0          0  MIPS GIC  63  IPI call
 10:          0    1696626          0          0  MIPS GIC  64  IPI call
 11:          0          0    2028319          0  MIPS GIC  65  IPI call
 12:          0          0          0    2274039  MIPS GIC  66  IPI call
 13:   36109948          0          0          0  MIPS GIC  67  IPI resched
 14:          0   37536459          0          0  MIPS GIC  68  IPI resched
 15:          0          0   64055102          0  MIPS GIC  69  IPI resched
 16:          0          0          0  108050864  MIPS GIC  70  IPI resched
 17:          0          0          0          0  MIPS GIC  19  1e000600.gpio-bank0, 1e000600.gpio-bank1, 1e000600.gpio-bank2
 19:         12          0          0          0  MIPS GIC  33  ttyS0
 20:          0          0          0          0  MIPS GIC  29  xhci-hcd:usb1
 21:    9926023          0          0          0  MIPS GIC  10  1e100000.ethernet
 23:         23          0  174641805          0  MIPS GIC  11  mt7603e
 24:         17          0          0   46926545  MIPS GIC  31  mt7615e
 26:          0          0          0          0  1e000600.gpio   8  keys
 27:          0          0          0          0  1e000600.gpio  10  keys
ERR:       8659
 OpenWrt 21.02.2, r16495-bf0c965af0

root@Archer_C6U:~# uptime
 21:16:22 up 16 days, 0 min,  load average: 0.04, 0.05, 0.00
root@Archer_C6U:~# uname -a
Linux Archer_C6U 5.4.179 #0 SMP Wed Feb 16 20:29:10 2022 mips GNU/Linux

Thanks for the Developers to fix this, and make this router usable with OpenWrt.