[LEDE-DEV] lantiq: reduced throughput with SMP disabled

[James Finnie]

It would be nice to get SMP enabled again for XRX200 - I've been
applying and running Felix's SMP enabling commit from his staging tree
for over a month now in a production (well my home) environment, with
no seeming ill-effect on HH5A.

Is the issue Antti mentioned blocking this?  Does it indicate that
running with SMP (while it seems to work) actually may do Bad Things
(TM)?


On 5 August 2016 at 12:57, Antti Seppälä <a.seppala at gmail.com> wrote:

> Hi Felix.
>
> I don't know if this is related or not but I've observed that if
> CONFIG_KERNEL_PROVE_LOCKING is enabled together with SMP the following
> kernel bug warning appears sometimes during nand probe in bootup
> (Zyxel P2812HNU-F1):
>
> [    0.872462] bootconsole [early0] disabled
> [    0.887856] BUG: spinlock wrong CPU on CPU#1, swapper/0/1
> [    0.892065]  lock: ebu_lock+0x0/0x20, .magic: dead4ead, .owner:
> swapper/0/1, .owner_cpu: 0
> [    0.900286] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.4.13 #1
> [    0.906101] Stack : 80f52c5a 00000033 0000004e 00000000 80f52c5a
> 00000000 80087498 00000000
>  878302f8 8064b493 805900fc 00000001 00000001 807a3a10 00000000 807a0000
>  00000008 80087498 00000000 00000000 80f52c5a 00000000 8059a2f0 87823c2c
>  80f52c5a 80084f98 80087498 00000040 87830000 00000000 80640000 87823c00
>  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>  ...
> [    0.941605] Call Trace:
> [    0.944080] [<8001c234>] show_stack+0x50/0x84
> [    0.948428] [<80213f0c>] dump_stack+0x128/0x1b0
> [    0.952962] [<80082c9c>] do_raw_spin_unlock+0xcc/0xfc
> [    0.958008] [<8000f174>] _raw_spin_unlock_irqrestore+0x30/0x88
> [    0.963851] [<802b35b0>] xway_nand_probe+0x12c/0x154
> [    0.968794] [<802b30f0>] plat_nand_probe+0x16c/0x25c
> [    0.973763] [<8028a960>] platform_drv_probe+0x28/0x6c
> [    0.978801] [<80288d0c>] driver_probe_device+0x220/0x4fc
> [    0.984111] [<80289068>] __driver_attach+0x80/0xb8
> [    0.988897] [<80286910>] bus_for_each_dev+0x64/0xc0
> [    0.993773] [<80287f78>] bus_add_driver+0x12c/0x284
> [    0.998647] [<80289688>] driver_register+0xac/0x104
> [    1.003526] [<8000fda0>] do_one_initcall+0x170/0x250
> [    1.008499] [<8066edf8>] kernel_init_freeable+0x174/0x244
> [    1.013891] [<80007260>] kernel_init+0x14/0x118
> [    1.018404] [<80002478>] ret_from_kernel_thread+0x14/0x1c
> [    1.023784]
> [    1.025428] nand: device found, Manufacturer ID: 0xec, Chip ID: 0xf1
> [    1.031618] nand: Samsung NAND 128MiB 3,3V 8-bit
> [    1.036239] nand: 128 MiB, SLC, erase size: 128 KiB, page size:
> 2048, OOB size: 64
>
> I guess that ebu_lock is not really smp safe for some reason.
>
> Br,
> -Antti