Re: PROBLEM: Only one CPU active on Ultra 60 since ~4.8 (regression)

[Nick Bowler]

Hi,

I'm resending this report CC'd to linux-kernel as there was no response
on the sparclinux list.

I tried 6.2-rc4 and there is no change in behaviour.  Reverting the
indicated commit still works to fix the problem.

On 2022-07-12, Nick Bowler <nbowler@xxxxxxxxxx> wrote:
> When using newer kernels on my Ultra 60 with dual 450MHz UltraSPARC-II
> CPUs, I noticed that only CPU 0 comes up, while older kernels (including
> 4.7) are working fine with both CPUs.
>
> I bisected the failure to this commit:
>
>   9b2f753ec23710aa32c0d837d2499db92fe9115b is the first bad commit
>   commit 9b2f753ec23710aa32c0d837d2499db92fe9115b
>   Author: Atish Patra <atish.patra@xxxxxxxxxx>
>   Date:   Thu Sep 15 14:54:40 2016 -0600
>
>       sparc64: Fix cpu_possible_mask if nr_cpus is set
>
> This is a small change that reverts very easily on top of 5.18: there is
> just one trivial conflict.  Once reverted, both CPUs work again.
>
> Maybe this is related to the fact that the CPUs on this system are
> numbered CPU0 and CPU2 (there is no CPU1)?
>
> Here is /proc/cpuinfo on a working kernel:
>
>     % cat /proc/cpuinfo
>     cpu             : TI UltraSparc II  (BlackBird)
>     fpu             : UltraSparc II integrated FPU
>     pmu             : ultra12
>     prom            : OBP 3.23.1 1999/07/16 12:08
>     type            : sun4u
>     ncpus probed    : 2
>     ncpus active    : 2
>     D$ parity tl1   : 0
>     I$ parity tl1   : 0
>     cpucaps         : flush,stbar,swap,muldiv,v9,mul32,div32,v8plus,vis
>     Cpu0ClkTck      : 000000001ad31b4f
>     Cpu2ClkTck      : 000000001ad31b4f
>     MMU Type        : Spitfire
>     MMU PGSZs       : 8K,64K,512K,4MB
>     State:
>     CPU0:           online
>     CPU2:           online
>
> And on a broken kernel:
>
>     % cat /proc/cpuinfo
>     cpu             : TI UltraSparc II  (BlackBird)
>     fpu             : UltraSparc II integrated FPU
>     pmu             : ultra12
>     prom            : OBP 3.23.1 1999/07/16 12:08
>     type            : sun4u
>     ncpus probed    : 2
>     ncpus active    : 1
>     D$ parity tl1   : 0
>     I$ parity tl1   : 0
>     cpucaps         : flush,stbar,swap,muldiv,v9,mul32,div32,v8plus,vis
>     Cpu0ClkTck      : 000000001ad31861
>     MMU Type        : Spitfire
>     MMU PGSZs       : 8K,64K,512K,4MB
>     State:
>     CPU0:           online
>
> Let me know if you need any more info.
>
> Thanks,
>   Nick