[PATCH v9 08/10] arm64: pmu: Detect and enable multiple PMUs in an ACPI system

[Punit Agrawal]

Jeremy Linton <jeremy.linton at arm.com> writes:

> Hi,
>
> On 09/16/2016 08:33 AM, Punit Agrawal wrote:
>> Jeremy Linton <jeremy.linton at arm.com> writes:
>>
>>> Its possible that an ACPI system has multiple CPU types in it
>>> with differing PMU counters. Iterate the CPU's and make a determination
>>> about how many of each type exist in the system. Then take and create
>>> a PMU platform device for each type, and assign it the interrupts parsed
>>> from the MADT. Creating a platform device is necessary because the PMUs
>>> are not described as devices in the DSDT table.
>>>
>>> This code is loosely based on earlier work by Mark Salter.
>
> (trimming)
>
>>> +
>>> +	list_for_each_entry_safe(pmu, safe_temp, &pmus, list) {
>>> +		if (unused_madt_entries)
>>> +			pmu->cpu_count = num_possible_cpus();
>>
>> So if there is any unbooted cpu ...
>>
>>> +
>>> +		res = kcalloc(pmu->cpu_count,
>>> +				  sizeof(struct resource), GFP_KERNEL);
>>
>> ... we allocate potentially large number (num_possible_cpus()) of
>> resources for each PMU.
>>
>> This is needlessly wasteful. Under what conditions have you found
>> reg_midr to be 0?
>
> Unused MADT entries, in place for potentially unbooted/hotplug
> CPUs.

Is linux able to deal with booting secondaries that have unused MADT
entries?

> In those cases you don't know for sure which PMU the CPU belongs
> to until it comes online and the MIDR can be read. I'm open to
> suggestions on how to deal with this, outside of pushing my luck and
> further breaking the platform device encapsulation by trying to
> reallocate the resource structure while its active. Besides its only
> wasteful for ACPI+big.little, which at the moment only applies to a
> development platform.

I don't have any ideas to solve this problem, but in the interest of
helping review, please move all the changes arising from hotplug/unused
MADT entries in this patch to the next one.

>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
> the body of a message to majordomo at vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html