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

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Date:   Tue, 29 May 2018 18:31:33 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Robin Murphy <robin.murphy@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Will Deacon <will.deacon@....com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Mark Rutland <Mark.Rutland@....com>, austinwc@...eaurora.org,
        tnowicki@...iumnetworks.com,
        Catalin Marinas <catalin.marinas@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        linux-riscv@...ts.infradead.org, wangxiongfeng2@...wei.com,
        vkilari@...eaurora.org,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        jhugo@...eaurora.org, Morten.Rasmussen@....com,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        John Garry <john.garry@...wei.com>, Al Stone <ahs3@...hat.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jeremy Linton <jeremy.linton@....com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Dietmar Eggemann <Dietmar.Eggemann@....com>
Subject: Re: [PATCH v9 00/12] Support PPTT for ARM64



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@....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@....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