* [PATCH 0/2] arm64/PPTT ACPI 6.3 thread flag support
@ 2019-05-23 22:40 Jeremy Linton
2019-05-23 22:40 ` [PATCH 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag Jeremy Linton
2019-05-23 22:40 ` [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread Jeremy Linton
0 siblings, 2 replies; 8+ messages in thread
From: Jeremy Linton @ 2019-05-23 22:40 UTC (permalink / raw)
To: linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, 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.
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 | 53 +++++++++++++++++++++++++++++++++++-
include/linux/acpi.h | 5 ++++
3 files changed, 62 insertions(+), 4 deletions(-)
--
2.21.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag
2019-05-23 22:40 [PATCH 0/2] arm64/PPTT ACPI 6.3 thread flag support Jeremy Linton
@ 2019-05-23 22:40 ` Jeremy Linton
2019-06-07 10:03 ` Sudeep Holla
2019-05-23 22:40 ` [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread Jeremy Linton
1 sibling, 1 reply; 8+ messages in thread
From: Jeremy Linton @ 2019-05-23 22:40 UTC (permalink / raw)
To: linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, 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 | 53 +++++++++++++++++++++++++++++++++++++++++++-
include/linux/acpi.h | 5 +++++
2 files changed, 57 insertions(+), 1 deletion(-)
diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index b72e6afaa8fb..6f43a0c05f61 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -517,6 +517,43 @@ 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.
+ * Otherwise returns flag value
+ */
+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 = -ENONET;
+
+ 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;
+
+ 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
@@ -581,6 +618,21 @@ int cache_setup_acpi(unsigned int cpu)
return status;
}
+/**
+ * acpi_pptt_cpu_is_thread() - Determine if logical 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
@@ -641,7 +693,6 @@ 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 98440df7fe42..513833233c65 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1314,10 +1314,15 @@ 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_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
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread
2019-05-23 22:40 [PATCH 0/2] arm64/PPTT ACPI 6.3 thread flag support Jeremy Linton
2019-05-23 22:40 ` [PATCH 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag Jeremy Linton
@ 2019-05-23 22:40 ` Jeremy Linton
2019-06-06 8:49 ` John Garry
1 sibling, 1 reply; 8+ messages in thread
From: Jeremy Linton @ 2019-05-23 22:40 UTC (permalink / raw)
To: linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, 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
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread
2019-05-23 22:40 ` [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread Jeremy Linton
@ 2019-06-06 8:49 ` John Garry
2019-06-07 19:21 ` Jeremy Linton
0 siblings, 1 reply; 8+ messages in thread
From: John Garry @ 2019-06-06 8:49 UTC (permalink / raw)
To: Jeremy Linton, linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, Linuxarm, Guohanjun (Hanjun Guo),
wanghuiqiang, yaohongbo
On 23/05/2019 23:40, 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.
>
Hi Jeremy,
I was just wondering if we should look to get this support backported
(when merged)?
I worry about the case of a system with the CPU having MT bit in the
MPIDR (while not actually threaded), i.e. the system for which these
PPTT flags were added (as I understand).
> 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;
For described above scenario, this seems wrong.
> topology_id = find_acpi_cpu_topology(cpu, 1);
>
BTW, we did test an old kernel with 6.3 PPTT bios for this on D06 (some
versions have MT bit set), and it looked ok. But I am still a bit skeptical.
Thanks,
John
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag
2019-05-23 22:40 ` [PATCH 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag Jeremy Linton
@ 2019-06-07 10:03 ` Sudeep Holla
0 siblings, 0 replies; 8+ messages in thread
From: Sudeep Holla @ 2019-06-07 10:03 UTC (permalink / raw)
To: Jeremy Linton
Cc: linux-arm-kernel, linux-acpi, catalin.marinas, will.deacon, rjw,
lenb, Sudeep Holla
On Thu, May 23, 2019 at 05:40:14PM -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.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
> drivers/acpi/pptt.c | 53 +++++++++++++++++++++++++++++++++++++++++++-
> include/linux/acpi.h | 5 +++++
> 2 files changed, 57 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index b72e6afaa8fb..6f43a0c05f61 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -517,6 +517,43 @@ 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.
> + * Otherwise returns flag value
> + */
> +static int check_acpi_cpu_flag(unsigned int cpu, int rev, u32 flag)
Initially, I thought we already have similar function, but I was wrong.
> +{
> + 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 = -ENONET;
Unfortunately even ENONET is defined and will silently compile fine, but
I assume you need ENOENT as mentioned in the comment/doc.
> +
> + 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;
> +
> + 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
> @@ -581,6 +618,21 @@ int cache_setup_acpi(unsigned int cpu)
> return status;
> }
>
> +/**
> + * acpi_pptt_cpu_is_thread() - Determine if logical 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
> @@ -641,7 +693,6 @@ int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
> return ret;
> }
>
> -
Spurious ?
> /**
> * 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 98440df7fe42..513833233c65 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1314,10 +1314,15 @@ 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_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
>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread
2019-06-06 8:49 ` John Garry
@ 2019-06-07 19:21 ` Jeremy Linton
2019-06-10 8:30 ` John Garry
0 siblings, 1 reply; 8+ messages in thread
From: Jeremy Linton @ 2019-06-07 19:21 UTC (permalink / raw)
To: John Garry, linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, Linuxarm, Guohanjun (Hanjun Guo),
wanghuiqiang, yaohongbo
Hi,
Thanks for testing and looking at this.
On 6/6/19 3:49 AM, John Garry wrote:
> On 23/05/2019 23:40, 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.
>>
>
> Hi Jeremy,
>
> I was just wondering if we should look to get this support backported
> (when merged)?
I imagine that will happen..
>
> I worry about the case of a system with the CPU having MT bit in the
> MPIDR (while not actually threaded), i.e. the system for which these
> PPTT flags were added (as I understand).
I have tested this patch on DAWN which happens to have the MT bit set,
but isn't threaded, and it appears to work.
>
>> 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;
>
> For described above scenario, this seems wrong.
I'm not sure I understand the concern.
This is going to ignore the MPIDR_MT bit on any machine with a PPTT
revision > 1. Are you worried about the topology_id assignment?
>
>> topology_id = find_acpi_cpu_topology(cpu, 1);
>>
>
> BTW, we did test an old kernel with 6.3 PPTT bios for this on D06 (some
> versions have MT bit set), and it looked ok. But I am still a bit
> skeptical.
>
> Thanks,
> John
>
>
Thanks,
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread
2019-06-07 19:21 ` Jeremy Linton
@ 2019-06-10 8:30 ` John Garry
2019-06-11 19:02 ` Jeremy Linton
0 siblings, 1 reply; 8+ messages in thread
From: John Garry @ 2019-06-10 8:30 UTC (permalink / raw)
To: Jeremy Linton, linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, Linuxarm, Guohanjun (Hanjun Guo),
wanghuiqiang, yaohongbo
On 07/06/2019 20:21, Jeremy Linton wrote:
> Hi,
>
> Thanks for testing and looking at this.
>
> On 6/6/19 3:49 AM, John Garry wrote:
>> On 23/05/2019 23:40, 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.
>>>
>>
Hi Jeremy,
>>
>> I was just wondering if we should look to get this support backported
>> (when merged)?
>
> I imagine that will happen..
>
>>
>> I worry about the case of a system with the CPU having MT bit in the
>> MPIDR (while not actually threaded), i.e. the system for which these
>> PPTT flags were added (as I understand).
>
> I have tested this patch on DAWN which happens to have the MT bit set,
> but isn't threaded, and it appears to work.
Can you describe your test?
>
>>
>>> 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;
>>
>> For described above scenario, this seems wrong.
>
> I'm not sure I understand the concern.
Maybe I wasn't clear enough previously. I am saying that without this
patch, then this info would not be correct. Hence the request to
backport to stable.
cheers,
>
> This is going to ignore the MPIDR_MT bit on any machine with a PPTT
> revision > 1. Are you worried about the topology_id assignment?
>
>
>>
>>> topology_id = find_acpi_cpu_topology(cpu, 1);
>>>
>>
>> BTW, we did test an old kernel with 6.3 PPTT bios for this on D06
>> (some versions have MT bit set), and it looked ok. But I am still a
>> bit skeptical.
>>
>> Thanks,
>> John
>>
>>
>
>
> Thanks,
>
> .
>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread
2019-06-10 8:30 ` John Garry
@ 2019-06-11 19:02 ` Jeremy Linton
0 siblings, 0 replies; 8+ messages in thread
From: Jeremy Linton @ 2019-06-11 19:02 UTC (permalink / raw)
To: John Garry, linux-arm-kernel
Cc: linux-acpi, catalin.marinas, will.deacon, rjw, lenb,
sudeep.holla, Linuxarm, Guohanjun (Hanjun Guo),
wanghuiqiang, yaohongbo
Hi,
On 6/10/19 3:30 AM, John Garry wrote:
> On 07/06/2019 20:21, Jeremy Linton wrote:
>> Hi,
>>
>> Thanks for testing and looking at this.
>>
>> On 6/6/19 3:49 AM, John Garry wrote:
>>> On 23/05/2019 23:40, 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.
>>>>
>>>
>
> Hi Jeremy,
>
>>>
>>> I was just wondering if we should look to get this support backported
>>> (when merged)?
>>
>> I imagine that will happen..
>>
>>>
>>> I worry about the case of a system with the CPU having MT bit in the
>>> MPIDR (while not actually threaded), i.e. the system for which these
>>> PPTT flags were added (as I understand).
>>
>> I have tested this patch on DAWN which happens to have the MT bit set,
>> but isn't threaded, and it appears to work.
>
> Can you describe your test?
The positive test:
Boot machine with/without patch, compare the output of lscpu & lstopo.
Manually check/compare /sys/devices/system/cpu/cpuX/topology/* and
/proc/schedstat domain masks. On DAWN we go from a system reporting 2
cores with 2 thread per core to 4 cores.
I've also built firmware or injected PPTT's with varying versions/etc to
sanity check cases that aren't representative of the hardware.
>
>>
>>>
>>>> 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;
>>>
>>> For described above scenario, this seems wrong.
>>
>> I'm not sure I understand the concern.
>
> Maybe I wasn't clear enough previously. I am saying that without this
> patch, then this info would not be correct. Hence the request to
> backport to stable.
>
> cheers,
>
>>
>> This is going to ignore the MPIDR_MT bit on any machine with a PPTT
>> revision > 1. Are you worried about the topology_id assignment?
>>
>>
>>>
>>>> topology_id = find_acpi_cpu_topology(cpu, 1);
>>>>
>>>
>>> BTW, we did test an old kernel with 6.3 PPTT bios for this on D06
>>> (some versions have MT bit set), and it looked ok. But I am still a
>>> bit skeptical.
>>>
>>> Thanks,
>>> John
>>>
>>>
>>
>>
>> Thanks,
>>
>> .
>>
>
>
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2019-06-11 19:06 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-23 22:40 [PATCH 0/2] arm64/PPTT ACPI 6.3 thread flag support Jeremy Linton
2019-05-23 22:40 ` [PATCH 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag Jeremy Linton
2019-06-07 10:03 ` Sudeep Holla
2019-05-23 22:40 ` [PATCH 2/2] arm64: topology: Use PPTT to determine if PE is a thread Jeremy Linton
2019-06-06 8:49 ` John Garry
2019-06-07 19:21 ` Jeremy Linton
2019-06-10 8:30 ` John Garry
2019-06-11 19:02 ` Jeremy Linton
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