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

[Linux kernel regression tracking (Thorsten Leemhuis)]

CCing the sparc maintainer. Also CCing the regression list, as it should
be in the loop for regressions:
https://docs.kernel.org/admin-guide/reporting-regressions.html

The the mail address of the culprit's author bounces. There is another
Atish Patra still active; does anyone known if those two are the same
person?

Anyway, that's it from my side.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

On 20.01.23 04:15, Nick Bowler wrote:
> 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
>