SMP on TD-W8980

root@ceres:~# /etc/init.d/dsl_control status
ATU-C Vendor ID:                          Broadcom 177.28
ATU-C System Vendor ID:                   Broadcom
Chipset:                                  Lantiq-VRX200 Unknown
Firmware Version:                         5.8.1.8.1.6
API Version:                              4.17.18.6
XTSE Capabilities:                        0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2
Annex:                                    B
Line Mode:                                G.993.2 (VDSL2)
Profile:                                  17a
Line State:                               UP [0x801: showtime_tc_sync]
Forward Error Correction Seconds (FECS):  Near: 0 / Far: 15478
Errored seconds (ES):                     Near: 0 / Far: 67
Severely Errored Seconds (SES):           Near: 0 / Far: 0
Loss of Signal Seconds (LOSS):            Near: 0 / Far: 0
Unavailable Seconds (UAS):                Near: 47 / Far: 47
Header Error Code Errors (HEC):           Near: 0 / Far: 0
Non Pre-emtive CRC errors (CRC_P):        Near: 0 / Far: 0
Pre-emtive CRC errors (CRCP_P):           Near: 0 / Far: 0
Power Management Mode:                    L0 - Synchronized
Latency [Interleave Delay]:               0.13 ms [Fast]   0.0 ms [Fast]
Data Rate:                                Down: 97.601 Mb/s / Up: 21.382 Mb/s
Line Attenuation (LATN):                  Down: 9.7 dB / Up: 10.9 dB
Signal Attenuation (SATN):                Down: 9.7 dB / Up: 10.7 dB
Noise Margin (SNR):                       Down: 6.2 dB / Up: 8.0 dB
Aggregate Transmit Power (ACTATP):        Down: -20.4 dB / Up: 11.8 dB
Max. Attainable Data Rate (ATTNDR):       Down: 101.405 Mb/s / Up: 26.854 Mb/s
Line Uptime Seconds:                      245329
Line Uptime:                              2d 20h 8m 49s

After some more tests I've found that interrupts don't get evenly distributed across available cores, with irqbalance being used or not:

> root@ceres:~# cat /proc/interrupts 
>            CPU0       CPU1                                                                                                                                                                                          
>   0:    1269944    3190965      MIPS   0  IPI_resched                                                                                                                                                               
>   1:     379636   12215401      MIPS   1  IPI_call                                                                                                                                                                  
>   7:   65161202   64454202      MIPS   7  timer                                                                                                                                                                     
>  22:    1601124          0       icu  22  spi_rx                                                                                                                                                                    
>  23:     106349          0       icu  23  spi_tx
>  24:          0          0       icu  24  spi_err
>  62:          0          0       icu  62  1e101000.ifxhcd, dwc2_hsotg:usb1
>  63:   13608652          0       icu  63  mei_cpe
>  72:   16459620          0       icu  72  vrx200_rx
>  73:   23624689          0       icu  73  vrx200_tx
>  75:          0          0       icu  75  vrx200_tx_2
>  91:    1007112          0       icu  91  1e106000.ifxhcd, dwc2_hsotg:usb2
>  96:   32790400          0       icu  96  ptm_mailbox_isr
> 112:       1491          0       icu 112  asc_tx
> 113:          0          0       icu 113  asc_rx
> 114:          0          0       icu 114  asc_err
> 126:          0          0       icu 126  gptu
> 127:          0          0       icu 127  gptu
> 128:          0          0       icu 128  gptu
> 129:          0          0       icu 129  gptu
> 130:          0          0       icu 130  gptu
> 131:          0          0       icu 131  gptu
> 144:   48007505          0       icu 144  ath9k
> 161:          0          0       icu 161  ifx_pcie_rc0
> ERR:          0

I don't have another router to test on but if I activate a pppoe connection from the PC where I am writing (vdsl interface is bridged on br-lan on the router), I can get stable 10-11MB/s downloads, whereas if it is the router to be used as pppoe client, the same download tests fluctuate between 6 and 8MB/s.

Edit: forgot to say that cpu load on the router is around 1-2% when idling