[PATCH v4 0/2] arm64/PPTT ACPI 6.3 thread flag support

[PATCH v4 0/2] arm64/PPTT ACPI 6.3 thread flag support

[Jeremy Linton]

ACPI 6.3 adds a flag to the CPU node to indicate whether
the given CPU is a thread. Add a function to return that
information for a given linux logical CPU and then utilize
it while building the arm64 topology.

v3->v4: Remove table revision cache as this code path is only
	       called during boot and there aren't any
	       indications that it presents a perf issue.
	Rebase to 5.3

v2->v3: Clarify and tweak the return from check_acpi_cpu_flag()
	Cache the PPTT table revision to avoid repeat
	      acpi_table_get/put calls in the case of
	      missing or old PPTT tables.

v1->v2:
	Return ENOENT instead on ENONET.

Jeremy Linton (2):
  ACPI/PPTT: Add support for ACPI 6.3 thread flag
  arm64: topology: Use PPTT to determine if PE is a thread

 arch/arm64/kernel/topology.c |  8 ++++--
 drivers/acpi/pptt.c          | 54 +++++++++++++++++++++++++++++++++++-
 include/linux/acpi.h         |  5 ++++
 3 files changed, 63 insertions(+), 4 deletions(-)

-- 
2.21.0

[PATCH v4 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

[Jeremy Linton]

ACPI 6.3 adds a flag to the CPU node to indicate whether
the given PE is a thread. Add a function to return that
information for a given linux logical CPU.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
---
 drivers/acpi/pptt.c  | 54 +++++++++++++++++++++++++++++++++++++++++++-
 include/linux/acpi.h |  5 ++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index 1e7ac0bd0d3a..84718f6cb741 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -540,6 +540,44 @@ static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
 	return retval;
 }
 
+/**
+ * check_acpi_cpu_flag() - Determine if CPU node has a flag set
+ * @cpu: Kernel logical CPU number
+ * @rev: The PPTT revision defining the flag
+ * @flag: The flag itself
+ *
+ * Check the node representing a CPU for a given flag.
+ *
+ * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found or
+ *	   the table revision isn't new enough.
+ *	   1, any passed flag set
+ *	   0, flag unset
+ */
+static int check_acpi_cpu_flag(unsigned int cpu, int rev, u32 flag)
+{
+	struct acpi_table_header *table;
+	acpi_status status;
+	u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
+	struct acpi_pptt_processor *cpu_node = NULL;
+	int ret = -ENOENT;
+
+	status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
+	if (ACPI_FAILURE(status)) {
+		acpi_pptt_warn_missing();
+		return ret;
+	}
+
+	if (table->revision >= rev)
+		cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
+
+	if (cpu_node)
+		ret = (cpu_node->flags & flag) != 0;
+
+	acpi_put_table(table);
+
+	return ret;
+}
+
 /**
  * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
  * @cpu: Kernel logical CPU number
@@ -604,6 +642,21 @@ int cache_setup_acpi(unsigned int cpu)
 	return status;
 }
 
+/**
+ * acpi_pptt_cpu_is_thread() - Determine if CPU is a thread
+ * @cpu: Kernel logical CPU number
+ *
+ *
+ * Return: 1, a thread
+ *         0, not a thread
+ *         -ENOENT ,if the PPTT doesn't exist, the CPU cannot be found or
+ *         the table revision isn't new enough.
+ */
+int acpi_pptt_cpu_is_thread(unsigned int cpu)
+{
+	return check_acpi_cpu_flag(cpu, 2, ACPI_PPTT_ACPI_PROCESSOR_IS_THREAD);
+}
+
 /**
  * find_acpi_cpu_topology() - Determine a unique topology value for a given CPU
  * @cpu: Kernel logical CPU number
@@ -664,7 +717,6 @@ int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
 	return ret;
 }
 
-
 /**
  * find_acpi_cpu_topology_package() - Determine a unique CPU package value
  * @cpu: Kernel logical CPU number
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 9426b9aaed86..9d0e20a2ac83 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1302,11 +1302,16 @@ static inline int lpit_read_residency_count_address(u64 *address)
 #endif
 
 #ifdef CONFIG_ACPI_PPTT
+int acpi_pptt_cpu_is_thread(unsigned int cpu);
 int find_acpi_cpu_topology(unsigned int cpu, int level);
 int find_acpi_cpu_topology_package(unsigned int cpu);
 int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
 int find_acpi_cpu_cache_topology(unsigned int cpu, int level);
 #else
+static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
+{
+	return -EINVAL;
+}
 static inline int find_acpi_cpu_topology(unsigned int cpu, int level)
 {
 	return -EINVAL;
-- 
2.21.0

[PATCH v4 2/2] arm64: topology: Use PPTT to determine if PE is a thread

[Jeremy Linton]

ACPI 6.3 adds a thread flag to represent if a CPU/PE is
actually a thread. Given that the MPIDR_MT bit may not
represent this information consistently on homogeneous machines
we should prefer the PPTT flag if its available.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
---
 arch/arm64/kernel/topology.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 0825c4a856e3..cbbedb53cf06 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -346,11 +346,9 @@ void remove_cpu_topology(unsigned int cpu)
  */
 static int __init parse_acpi_topology(void)
 {
-	bool is_threaded;
+	int is_threaded;
 	int cpu, topology_id;
 
-	is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
-
 	for_each_possible_cpu(cpu) {
 		int i, cache_id;
 
@@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void)
 		if (topology_id < 0)
 			return topology_id;
 
+		is_threaded = acpi_pptt_cpu_is_thread(cpu);
+		if (is_threaded < 0)
+			is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
+
 		if (is_threaded) {
 			cpu_topology[cpu].thread_id = topology_id;
 			topology_id = find_acpi_cpu_topology(cpu, 1);
-- 
2.21.0

Re: [PATCH v4 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

[Sudeep Holla]

Hi Jeremy,

On Wed, Jul 31, 2019 at 10:46:33PM -0500, Jeremy Linton wrote:
> ACPI 6.3 adds a flag to the CPU node to indicate whether
> the given PE is a thread. Add a function to return that
> information for a given linux logical CPU.
>

Apart from few minor nits,

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  drivers/acpi/pptt.c  | 54 +++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/acpi.h |  5 ++++
>  2 files changed, 58 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 1e7ac0bd0d3a..84718f6cb741 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -540,6 +540,44 @@ static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
>  	return retval;
>  }
>
> +/**
> + * check_acpi_cpu_flag() - Determine if CPU node has a flag set
> + * @cpu: Kernel logical CPU number
> + * @rev: The PPTT revision defining the flag

[nit] I would rather put it as minimum PPTT revision that supports the
flag. It aligns with the code too as we are not looking for exact match.

> + * @flag: The flag itself
> + *
> + * Check the node representing a CPU for a given flag.
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found or
> + *	   the table revision isn't new enough.
> + *	   1, any passed flag set
> + *	   0, flag unset
> + */
> +static int check_acpi_cpu_flag(unsigned int cpu, int rev, u32 flag)
> +{
> +	struct acpi_table_header *table;
> +	acpi_status status;
> +	u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> +	struct acpi_pptt_processor *cpu_node = NULL;
> +	int ret = -ENOENT;
> +
> +	status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
> +	if (ACPI_FAILURE(status)) {
> +		acpi_pptt_warn_missing();
> +		return ret;
> +	}
> +
> +	if (table->revision >= rev)
> +		cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
> +
> +	if (cpu_node)
> +		ret = (cpu_node->flags & flag) != 0;
> +
> +	acpi_put_table(table);
> +
> +	return ret;
> +}
> +
>  /**
>   * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
>   * @cpu: Kernel logical CPU number
> @@ -604,6 +642,21 @@ int cache_setup_acpi(unsigned int cpu)
>  	return status;
>  }
>
> +/**
> + * acpi_pptt_cpu_is_thread() - Determine if CPU is a thread
> + * @cpu: Kernel logical CPU number
> + *

[nit] If you spin the patch again, you can drop extra line space here.

--
Regards,
Sudeep

Re: [PATCH v4 2/2] arm64: topology: Use PPTT to determine if PE is a thread

[Sudeep Holla]

On Wed, Jul 31, 2019 at 10:46:34PM -0500, Jeremy Linton wrote:
> ACPI 6.3 adds a thread flag to represent if a CPU/PE is
> actually a thread. Given that the MPIDR_MT bit may not
> represent this information consistently on homogeneous machines
> we should prefer the PPTT flag if its available.
>

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

--
Regards,
Sudeep

Re: [PATCH v4 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

[Jeremy Linton]

Hi,


Thanks for looking at this.

On 8/1/19 10:57 AM, Sudeep Holla wrote:
> 
> Hi Jeremy,
> 
> On Wed, Jul 31, 2019 at 10:46:33PM -0500, Jeremy Linton wrote:
>> ACPI 6.3 adds a flag to the CPU node to indicate whether
>> the given PE is a thread. Add a function to return that
>> information for a given linux logical CPU.
>>
> 
> Apart from few minor nits,
> 
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> 
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>>   drivers/acpi/pptt.c  | 54 +++++++++++++++++++++++++++++++++++++++++++-
>>   include/linux/acpi.h |  5 ++++
>>   2 files changed, 58 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>> index 1e7ac0bd0d3a..84718f6cb741 100644
>> --- a/drivers/acpi/pptt.c
>> +++ b/drivers/acpi/pptt.c
>> @@ -540,6 +540,44 @@ static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
>>   	return retval;
>>   }
>>
>> +/**
>> + * check_acpi_cpu_flag() - Determine if CPU node has a flag set
>> + * @cpu: Kernel logical CPU number
>> + * @rev: The PPTT revision defining the flag
> 
> [nit] I would rather put it as minimum PPTT revision that supports the
> flag. It aligns with the code too as we are not looking for exact match.

Ok, sure.


> 
>> + * @flag: The flag itself
>> + *
>> + * Check the node representing a CPU for a given flag.
>> + *
>> + * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found or
>> + *	   the table revision isn't new enough.
>> + *	   1, any passed flag set
>> + *	   0, flag unset
>> + */
>> +static int check_acpi_cpu_flag(unsigned int cpu, int rev, u32 flag)
>> +{
>> +	struct acpi_table_header *table;
>> +	acpi_status status;
>> +	u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
>> +	struct acpi_pptt_processor *cpu_node = NULL;
>> +	int ret = -ENOENT;
>> +
>> +	status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
>> +	if (ACPI_FAILURE(status)) {
>> +		acpi_pptt_warn_missing();
>> +		return ret;
>> +	}
>> +
>> +	if (table->revision >= rev)
>> +		cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
>> +
>> +	if (cpu_node)
>> +		ret = (cpu_node->flags & flag) != 0;
>> +
>> +	acpi_put_table(table);
>> +
>> +	return ret;
>> +}
>> +
>>   /**
>>    * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
>>    * @cpu: Kernel logical CPU number
>> @@ -604,6 +642,21 @@ int cache_setup_acpi(unsigned int cpu)
>>   	return status;
>>   }
>>
>> +/**
>> + * acpi_pptt_cpu_is_thread() - Determine if CPU is a thread
>> + * @cpu: Kernel logical CPU number
>> + *
> 
> [nit] If you spin the patch again, you can drop extra line space here.

Sure..


> 
> --
> Regards,
> Sudeep
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

Re: [PATCH v4 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

[Robert Richter]

On 31.07.19 22:46:33, Jeremy Linton wrote:

> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 9426b9aaed86..9d0e20a2ac83 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1302,11 +1302,16 @@ static inline int lpit_read_residency_count_address(u64 *address)
>  #endif
>  
>  #ifdef CONFIG_ACPI_PPTT
> +int acpi_pptt_cpu_is_thread(unsigned int cpu);
>  int find_acpi_cpu_topology(unsigned int cpu, int level);
>  int find_acpi_cpu_topology_package(unsigned int cpu);
>  int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
>  int find_acpi_cpu_cache_topology(unsigned int cpu, int level);

All those functions (exept hetero_id) are used only in
parse_acpi_topology(). So how about creating a struct with thread_id,
core_id, and cache_id (and hetero_id (?)) and have a single pptt table
parsing function that fills in all of this into that struct? This
simplifies the api and also the code.

This also shows that hetid (see arm_pmu_acpi.c) better should be
stored in cpu_topology[] too and thus being parsed with the other
parameters as well and made accessible from there by a helper.

-Robert

Re: [PATCH v4 2/2] arm64: topology: Use PPTT to determine if PE is a thread

[Robert Richter]

On 31.07.19 22:46:34, Jeremy Linton wrote:

> @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void)
>  		if (topology_id < 0)
>  			return topology_id;
>  
> +		is_threaded = acpi_pptt_cpu_is_thread(cpu);
> +		if (is_threaded < 0)
> +			is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
> +

I think the return code handling is error-prone, as in the kernel such
functions are typically used like:

	if (something_is_thread) { ... }

I see this is due to acpi and arch code separation so we cannot simply
move the fallback to pptt code.

So maybe we have a static function cpu_is_thread() in this file that
handles all the logic and directly use check_acpi_cpu_flag() from
there. However, code may change here in case of a rework as I
suggested in patch #1. In both cases the acpi api is more straight
then.

-Robert

>  		if (is_threaded) {
>  			cpu_topology[cpu].thread_id = topology_id;
>  			topology_id = find_acpi_cpu_topology(cpu, 1);

Re: [PATCH v4 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

[Jeremy Linton]

Hi,

Thanks for taking a look at this.

On 8/2/19 8:05 AM, Robert Richter wrote:
> On 31.07.19 22:46:33, Jeremy Linton wrote:
> 
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index 9426b9aaed86..9d0e20a2ac83 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -1302,11 +1302,16 @@ static inline int lpit_read_residency_count_address(u64 *address)
>>   #endif
>>   
>>   #ifdef CONFIG_ACPI_PPTT
>> +int acpi_pptt_cpu_is_thread(unsigned int cpu);
>>   int find_acpi_cpu_topology(unsigned int cpu, int level);
>>   int find_acpi_cpu_topology_package(unsigned int cpu);
>>   int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
>>   int find_acpi_cpu_cache_topology(unsigned int cpu, int level);
> 
> All those functions (exept hetero_id) are used only in
> parse_acpi_topology(). So how about creating a struct with thread_id,
> core_id, and cache_id (and hetero_id (?)) and have a single pptt table
> parsing function that fills in all of this into that struct? This
> simplifies the api and also the code.
> 
> This also shows that hetid (see arm_pmu_acpi.c) better should be
> stored in cpu_topology[] too and thus being parsed with the other
> parameters as well and made accessible from there by a helper.


I think the idea here was to avoid an additional set of intermediate 
data structures between the PPTT table/structure and the final arch 
specific data structures (which themselves are used to feed other 
things, like the scheduler, note the llc parsing). Rather the attempt is 
to provide a set of tools to retrieve information and let the policy for 
how that information is used be dictated by the consumer.

In the future, if we can further unify the arch specific cpu_topology 
structures it would make sense to parse directly into them, but until 
that happens I don't think we should try. The existing code does parse 
directly into the cache structures, but the cpu topology is subtly arm64 
at the moment. If another arch decided to use this, i'm not sure they 
would want or need it parsed in exactly the same way.

Re: [PATCH v4 2/2] arm64: topology: Use PPTT to determine if PE is a thread

[Jeremy Linton]

Hi,


On 8/2/19 8:44 AM, Robert Richter wrote:
> On 31.07.19 22:46:34, Jeremy Linton wrote:
> 
>> @@ -358,6 +356,10 @@ static int __init parse_acpi_topology(void)
>>   		if (topology_id < 0)
>>   			return topology_id;
>>   
>> +		is_threaded = acpi_pptt_cpu_is_thread(cpu);
>> +		if (is_threaded < 0)
>> +			is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
>> +
> 
> I think the return code handling is error-prone, as in the kernel such
> functions are typically used like:
> 
> 	if (something_is_thread) { ... }

I don't really understand why this keeps getting repeated. The negative 
error code return is used by huge swaths of the kernel API. A couple 
lines up the exact same paradigm is used in get_cpu_for_node() and a few 
other places.

> 
> I see this is due to acpi and arch code separation so we cannot simply
> move the fallback to pptt code.

Right, the PPTT->arch data structure translation is arch specific. 
During the initial PPTT drop a lot of discussion when into how arm64 was 
doing that translation, as well as the corresponding translation to the 
core scheduler/etc.

> 
> So maybe we have a static function cpu_is_thread() in this file that
> handles all the logic and directly use check_acpi_cpu_flag() from
> there. However, code may change here in case of a rework as I
> suggested in patch #1. In both cases the acpi api is more straight
> then.

I'm ok with that, it effectively only moves those three lines to a 
standalone single call-site function. To be clear, that isn't a generic 
routine for anyone to call. Functions that need to know if the core is a 
threaded should be checking the topology thread_id directly rather than 
re-coding the acpi/dt/mpidr logic which populates it.


> 
> -Robert
> 
>>   		if (is_threaded) {
>>   			cpu_topology[cpu].thread_id = topology_id;
>>   			topology_id = find_acpi_cpu_topology(cpu, 1);

Re: [PATCH v4 2/2] arm64: topology: Use PPTT to determine if PE is a thread

[Robert Richter]

On 08.08.19 15:40:07, Jeremy Linton wrote:
> ACPI 6.3 adds a thread flag to represent if a CPU/PE is
> actually a thread. Given that the MPIDR_MT bit may not
> represent this information consistently on homogeneous machines
> we should prefer the PPTT flag if its available.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
>  arch/arm64/kernel/topology.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 0825c4a856e3..bad9c42ea825 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -340,17 +340,28 @@ void remove_cpu_topology(unsigned int cpu)
>  }
>  
>  #ifdef CONFIG_ACPI
> +static int __init acpi_cpu_is_threaded(int cpu)
> +{
> +	int is_threaded = acpi_pptt_cpu_is_thread(cpu);
> +
> +	/*
> +	 * if the PPTT doesn't have thread information, assume a homogeneous
> +	 * machine and return the current CPU's thread state.
> +	 */
> +	if (is_threaded < 0)
> +		is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;

Since this is no longer bool now, better have a !!(...) or (...) != 0
here.

> +
> +	return is_threaded;
> +}
> +
>  /*
>   * Propagate the topology information of the processor_topology_node tree to the
>   * cpu_topology array.
>   */
>  static int __init parse_acpi_topology(void)
>  {
> -	bool is_threaded;
>  	int cpu, topology_id;
>  
> -	is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
> -
>  	for_each_possible_cpu(cpu) {
>  		int i, cache_id;
>  
> @@ -358,7 +369,7 @@ static int __init parse_acpi_topology(void)
>  		if (topology_id < 0)
>  			return topology_id;
>  
> -		if (is_threaded) {
> +		if (acpi_cpu_is_threaded(cpu)) {
>  			cpu_topology[cpu].thread_id = topology_id;
>  			topology_id = find_acpi_cpu_topology(cpu, 1);
>  			cpu_topology[cpu].core_id   = topology_id;

Looks otherwise ok.

Reviewed-by: Robert Richter <rrichter@marvell.com>

[PATCH v4 2/2] arm64: topology: Use PPTT to determine if PE is a thread

[Jeremy Linton]

ACPI 6.3 adds a thread flag to represent if a CPU/PE is
actually a thread. Given that the MPIDR_MT bit may not
represent this information consistently on homogeneous machines
we should prefer the PPTT flag if its available.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
---
 arch/arm64/kernel/topology.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 0825c4a856e3..bad9c42ea825 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -340,17 +340,28 @@ void remove_cpu_topology(unsigned int cpu)
 }
 
 #ifdef CONFIG_ACPI
+static int __init acpi_cpu_is_threaded(int cpu)
+{
+	int is_threaded = acpi_pptt_cpu_is_thread(cpu);
+
+	/*
+	 * if the PPTT doesn't have thread information, assume a homogeneous
+	 * machine and return the current CPU's thread state.
+	 */
+	if (is_threaded < 0)
+		is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
+
+	return is_threaded;
+}
+
 /*
  * Propagate the topology information of the processor_topology_node tree to the
  * cpu_topology array.
  */
 static int __init parse_acpi_topology(void)
 {
-	bool is_threaded;
 	int cpu, topology_id;
 
-	is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
-
 	for_each_possible_cpu(cpu) {
 		int i, cache_id;
 
@@ -358,7 +369,7 @@ static int __init parse_acpi_topology(void)
 		if (topology_id < 0)
 			return topology_id;
 
-		if (is_threaded) {
+		if (acpi_cpu_is_threaded(cpu)) {
 			cpu_topology[cpu].thread_id = topology_id;
 			topology_id = find_acpi_cpu_topology(cpu, 1);
 			cpu_topology[cpu].core_id   = topology_id;
-- 
2.21.0