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

[Nick Bowler]

Hi,

Just a friendly reminder that this issue still happens on Linux 6.8 and
reverting commit 9b2f753ec237 as indicated below is still sufficient to
resolve the problem.

On 2023-01-21 08:31, Linux kernel regression tracking (Thorsten Leemhuis) wrote:
> 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.
[...]
> 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