Re: [PATCH v9 00/12] Support PPTT for ARM64

Sudeep Holla
2018-05-29T17:31:44Z

On 29/05/18 18:08, Robin Murphy wrote:
> On 29/05/18 16:51, Geert Uytterhoeven wrote:
>> Hi Will,
>>
>> On Tue, May 29, 2018 at 5:08 PM, Will Deacon <will.deacon@arm.com> wrote:
>>> On Tue, May 29, 2018 at 02:18:40PM +0100, Sudeep Holla wrote:
>>>> On 29/05/18 12:56, Geert Uytterhoeven wrote:
>>>>> On Tue, May 29, 2018 at 1:14 PM, Sudeep Holla
>>>>> <sudeep.holla@arm.com> wrote:
>>>>>> On 29/05/18 11:48, Geert Uytterhoeven wrote:
>>>>>>> System supend still works fine on systems with big cores only:
>>>>>>>
>>>>>>>      R-Car H3 ES1.0 (4xCA57 (4xCA53 disabled in firmware))
>>>>>>>      R-Car M3-N (2xCA57)
>>>>>>>
>>>>>>> Reverting this commit fixes the issue for me.
>>>>>>
>>>>>> I can't find anything that relates to system suspend in these patches
>>>>>> unless they are messing with something during CPU hot plug-in back
>>>>>> during resume.
>>>>>
>>>>> It's only the last patch that introduces the breakage.
>>>>>
>>>>
>>>> As specified in the commit log, it won't change any behavior for DT
>>>> systems if it's non-NUMA or single node system. So I am still wondering
>>>> what could trigger this regression.
>>>
>>> I wonder if we're somehow giving an uninitialised/invalid NUMA
>>> configuration
>>> to the scheduler, although I can't see how this would happen.
>>>
>>> Geert -- if you enable CONFIG_DEBUG_PER_CPU_MAPS=y and apply the diff
>>> below
>>> do you see anything shouting in dmesg?
>>
>> Thanks, but unfortunately it doesn't help.
>> I added some debug code to print cpumask, but so far I don't see anything
>> suspicious.
>
> Do you have CONFIG_NUMA enabled? On a hunch I've managed to reproduce
> what looks like the same thing on a Juno board with NUMA=n; going in
> with external debug it seems to be stuck in the loop in
> init_sched_groups_capacity(), with an approximate stack trace of:
>
>
> init_sched_groups_capacity()
> partition_sched_domains()
> cpuset_cpu_active()
> sched_cpu_activate()
> cpuhp_invoke_callback()
> cpuhp_thread_fn()
>
> My hunch is based on the fact that it looks like we can, under the right
> circumstances, end up with default_topology picking up cpu_online_mask
> as a sibling mask via cpu_coregroup_mask(), and given the great
> coincidence that that's going to change when hotplugging out CPUs on
> suspend, things might not react too well to that. Things also look to go
> utterly haywire once into a full-blown systemd userspace with cpuidle,
> but I haven't got a clear picture of that yet.
>

Yes, I too observed the same. I was able to suspend resume if I have
cpuidle disabled.

--
Regards,
Sudeep