arm64: topology: add MPIDR-based detection

From: Zi Shen Lim <[email protected]>

Create cpu topology based on MPIDR. When hardware sets MPIDR to sane values, this method will always work. Therefore it should also work well as the fallback method. [1]

When we have multiple processing elements in the system, we create the cpu topology by mapping each affinity level (from lowest to highest) to threads (if they exist), cores, and clusters.

We combine data from all higher affinity levels into cluster_id so we don't lose any information from MPIDR. [2]

[1] http://www.spinics.net/lists/arm-kernel/msg317445.html
[2] https://lkml.org/lkml/2014/4/23/703

Signed-off-by Zi Shen Lim <[email protected]>

Signed-off-by Mark Brown <[email protected]>

---
 arch/arm64/include/asm/cputype.h |  2 ++
 arch/arm64/kernel/topology.c     | 51 +++++++++++++++++++++++++++++-----------
 2 files changed, 39 insertions(+), 14 deletions(-)

arch/arm64/include/asm/cputype.h +2 -0

index 27f54a7cc81b..ed48a3a7836a 100644
@@ -18,6 +18,8 @@
 
 #define INVALID_HWID		ULONG_MAX
 
+#define MPIDR_UP_BITMASK	(0x1 << 30)
+#define MPIDR_MT_BITMASK	(0x1 << 24)
 #define MPIDR_HWID_BITMASK	0xff00ffffff
 
 #define MPIDR_LEVEL_BITS_SHIFT	3

arch/arm64/kernel/topology.c +37 -14

index 43514f905916..9a0160068503 100644
@@ -20,6 +20,7 @@
 #include <linux/of.h>
 #include <linux/sched.h>
 
+#include <asm/cputype.h>
 #include <asm/topology.h>
 
 static int __init get_cpu_for_node(struct device_node *node)

@@ -188,13 +189,9 @@ static int __init parse_dt_topology(void)
 	 * Check that all cores are in the topology; the SMP code will
 	 * only mark cores described in the DT as possible.
 	 */
-	for_each_possible_cpu(cpu) {
-		if (cpu_topology[cpu].cluster_id == -1) {
-			pr_err("CPU%d: No topology information specified\n",
-			       cpu);
+	for_each_possible_cpu(cpu)
+		if (cpu_topology[cpu].cluster_id == -1)
 			ret = -EINVAL;
-		}
-	}
 
 out_map:
 	of_node_put(map);

@@ -219,14 +216,6 @@ static void update_siblings_masks(unsigned int cpuid)
 	struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
 	int cpu;
 
-	if (cpuid_topo->cluster_id == -1) {
-		/*
-		 * DT does not contain topology information for this cpu.
-		 */
-		pr_debug("CPU%u: No topology information configured\n", cpuid);
-		return;
-	}
-
 	/* update core and thread sibling masks */
 	for_each_possible_cpu(cpu) {
 		cpu_topo = &cpu_topology[cpu];

@@ -249,6 +238,40 @@ static void update_siblings_masks(unsigned int cpuid)
 
 void store_cpu_topology(unsigned int cpuid)
 {
+	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
+	u64 mpidr;
+
+	if (cpuid_topo->cluster_id != -1)
+		goto topology_populated;
+
+	mpidr = read_cpuid_mpidr();
+
+	/* Create cpu topology mapping based on MPIDR. */
+	if (mpidr & MPIDR_UP_BITMASK) {
+		/* Uniprocessor system */
+		cpuid_topo->thread_id  = -1;
+		cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+		cpuid_topo->cluster_id = 0;
+	} else if (mpidr & MPIDR_MT_BITMASK) {
+		/* Multiprocessor system : Multi-threads per core */
+		cpuid_topo->thread_id  = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+		cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+		cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 2) |
+					 MPIDR_AFFINITY_LEVEL(mpidr, 3) << 8;
+	} else {
+		/* Multiprocessor system : Single-thread per core */
+		cpuid_topo->thread_id  = -1;
+		cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+		cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 1) |
+					 MPIDR_AFFINITY_LEVEL(mpidr, 2) << 8 |
+					 MPIDR_AFFINITY_LEVEL(mpidr, 3) << 16;
+	}
+
+	pr_debug("CPU%u: cluster %d core %d thread %d mpidr %llx\n",
+		 cpuid, cpuid_topo->cluster_id, cpuid_topo->core_id,
+		 cpuid_topo->thread_id, mpidr);
+
+topology_populated:
 	update_siblings_masks(cpuid);
 }
 

Signature · 1 line

2.0.0.rc4

I refactored the patch (UP code path) and deliberately removed the code that packs affinity levels into the cluster id. I do not like packing the affinity levels and on second thoughts packing the unused affinity levels into cluster_id is as correct as packing the unused affinity levels into core_id (ie it is arbitrary), so I do

not think we should do it, that's the reason why we defined DT bindings to add a proper topology semantics and we should use them when the MPIDR values deviate from the "recommendations".

Patch attached, my ack included, should be ready to go, unless you object to that.

Quoted 5 lines · Lorenzo Pieralisi

I refactored the patch (UP code path) and deliberately removed the code that packs affinity levels into the cluster id. I do not like packing the affinity levels and on second thoughts packing the unused affinity levels into cluster_id is as correct as packing the unused affinity levels into core_id (ie it is arbitrary), so I do

I'm having a really hard time seeing this as anything other than a step back. Your change causes us to discard the higher affinity levels which seems like something we actively know to be misleading and means that we will be handing the scheduler two different identically numbered cores (all the affinity levels we do pay attention to will be identical) if we ever encounter such a system which is actively broken.

Quoted 3 lines

not think we should do it, that's the reason why we defined DT bindings to add a proper topology semantics and we should use them when the MPIDR values deviate from the "recommendations".

I'd agree with not going to great lengths unless someone defines semantics for the higher affinity levels in the future however it does seem like completely ignoring them when it's so easy to take some account of them is insufficiently defensive - it's similar to things like putting the of_node_put() calls in even though they don't do anything at the minute.

Quoted 2 lines

Patch attached, my ack included, should be ready to go, unless you object to that.

Well, I certainly don't object to getting something merged here.

Quoted 6 lines · Mark Brown

I'm having a really hard time seeing this as anything other than a step back. Your change causes us to discard the higher affinity levels which seems like something we actively know to be misleading and means that we will be handing the scheduler two different identically numbered cores (all the affinity levels we do pay attention to will be identical) if we ever encounter such a system which is actively broken.

If we ever encounter such systems we will deal with them when time comes, DT can handle them and patching this code is trivial.

All I am saying is, let's wait and see, there is no compelling need to use aff3 (and aff2 on non-SMT systems) on current systems for the topology.

Quoted 3 lines

Quoted 3 lines

not think we should do it, that's the reason why we defined DT bindings to add a proper topology semantics and we should use them when the MPIDR values deviate from the "recommendations".

Quoted 6 lines

I'd agree with not going to great lengths unless someone defines semantics for the higher affinity levels in the future however it does seem like completely ignoring them when it's so easy to take some account of them is insufficiently defensive - it's similar to things like putting the of_node_put() calls in even though they don't do anything at the minute.

So why don't you remove of_node_put() all over the kernel then ?

Quoted 11 lines · Lorenzo Pieralisi

Quoted 6 lines · Mark Brown

I'm having a really hard time seeing this as anything other than a step back. Your change causes us to discard the higher affinity levels which seems like something we actively know to be misleading and means that we will be handing the scheduler two different identically numbered cores (all the affinity levels we do pay attention to will be identical) if we ever encounter such a system which is actively broken.

If we ever encounter such systems we will deal with them when time comes, DT can handle them and patching this code is trivial.

Quoted 3 lines

All I am saying is, let's wait and see, there is no compelling need to use aff3 (and aff2 on non-SMT systems) on current systems for the topology.

That's still a kernel patch or having to write DT to get things working which for the sake of avoiding a couple of shift and or statements just seems unhelpful. If it was just going to give poor performance that'd be one thing but it's actively broken.

Quoted 2 lines · Mark Brown

Quoted 2 lines

All I am saying is, let's wait and see, there is no compelling need to use aff3 (and aff2 on non-SMT systems) on current systems for the

Quoted 4 lines

That's still a kernel patch or having to write DT to get things working which for the sake of avoiding a couple of shift and or statements just seems unhelpful. If it was just going to give poor performance that'd be one thing but it's actively broken.

What's broken ? Please provide me with an example and I will update the patch.

Quoted 9 lines · Lorenzo Pieralisi

Quoted 7 lines · Mark Brown

Quoted 2 lines

All I am saying is, let's wait and see, there is no compelling need to use aff3 (and aff2 on non-SMT systems) on current systems for the

That's still a kernel patch or having to write DT to get things working which for the sake of avoiding a couple of shift and or statements just seems unhelpful. If it was just going to give poor performance that'd be one thing but it's actively broken.

Quoted 2 lines

What's broken ? Please provide me with an example and I will update the patch.

If some system we encounter in the future is for example a SMT system which does use aff3 then until someone actively goes and fixes it by writing the DT/ACPI or updating the kernel if there's two threads 0,0,0,0 and 0,0,0,1 we'll tell the scheduler they're both 0,0,0 which we're not supposed to do.

My question is: is it better to pack affinity levels and "guess" what aff3 (and aff2 on non-SMT) means or add an additional level of hierarchy in the arm64 topology code (eg book_id - implemented only for s390 to the best of my knowledge) ?

I personally prefer the latter approach but I think it boils down to understanding what do we want to provide the scheduler with if we have a hierarchy that extends beyond "cluster" level.

I will be glad to help you implement it when time comes (and this will also fix the clusters of clusters DT issue we are facing - ie how to treat them).

Now, I do not think it is a major problem at the moment, merging the patch I sent will give us more time to discuss how to define the topology for clusters of clusters, because that's what we are talking about.

Does it make sense ?

Quoted 4 lines · Lorenzo Pieralisi

My question is: is it better to pack affinity levels and "guess" what aff3 (and aff2 on non-SMT) means or add an additional level of hierarchy in the arm64 topology code (eg book_id - implemented only for s390 to the best of my knowledge) ?

Shoving them in there would address the issue as well, yes (though we'd still have to combine aff2 and aff3 for the non-SMT case). I don't know if having books enabled has some overhead we don't want though.

Quoted 11 lines

I personally prefer the latter approach but I think it boils down to understanding what do we want to provide the scheduler with if we have a hierarchy that extends beyond "cluster" level.

I will be glad to help you implement it when time comes (and this will also fix the clusters of clusters DT issue we are facing - ie how to treat them).

Now, I do not think it is a major problem at the moment, merging the patch I sent will give us more time to discuss how to define the topology for clusters of clusters, because that's what we are talking about.

In so far as you're saying that we don't really need to worry about exactly how we handle multi-level clusters properly at the minute I agree with you - until we have some idea what they physically look like and can consider how well that maps onto the scheduler and whatnot it doesn't really matter and we can just ignore it. Given that I'm not concerned about just reporting everything as flat like we do with DT at the minute and don't see a real need to theorise about it, it'll just be a performance problem and not a correctness problem when it is encountered. That feels like a better position to leave things in as it will be less stress for whoever is bringing up such a fancy new system, they can stand a reasonable chance of getting things at least running with minimal effort.

Quoted 1 line

Does it make sense ?

Like I say I do think that merging your current code is better than nothing.

Quoted 23 lines · Mark Brown

Quoted 4 lines · Lorenzo Pieralisi

My question is: is it better to pack affinity levels and "guess" what aff3 (and aff2 on non-SMT) means or add an additional level of hierarchy in the arm64 topology code (eg book_id - implemented only for s390 to the best of my knowledge) ?

Shoving them in there would address the issue as well, yes (though we'd still have to combine aff2 and aff3 for the non-SMT case). I don't know if having books enabled has some overhead we don't want though.

Quoted 11 lines

I personally prefer the latter approach but I think it boils down to understanding what do we want to provide the scheduler with if we have a hierarchy that extends beyond "cluster" level.

I will be glad to help you implement it when time comes (and this will also fix the clusters of clusters DT issue we are facing - ie how to treat them).

Now, I do not think it is a major problem at the moment, merging the patch I sent will give us more time to discuss how to define the topology for clusters of clusters, because that's what we are talking about.

Quoted 12 lines

In so far as you're saying that we don't really need to worry about exactly how we handle multi-level clusters properly at the minute I agree with you - until we have some idea what they physically look like and can consider how well that maps onto the scheduler and whatnot it doesn't really matter and we can just ignore it. Given that I'm not concerned about just reporting everything as flat like we do with DT at the minute and don't see a real need to theorise about it, it'll just be a performance problem and not a correctness problem when it is encountered. That feels like a better position to leave things in as it will be less stress for whoever is bringing up such a fancy new system, they can stand a reasonable chance of getting things at least running with minimal effort.

Ok, I think we have an agreement, let's merge the patch I sent and discuss the way forward to cater for systems with clusters of clusters when we reasonably expect them to hit production, the scheduler expected topology might well change by that time and now we are well positioned to cope with future extensions (and actually packing affinity levels might well be the final solution if the scheduler expects a "flat" topology at the higher topology level).

Quoted 4 lines

Quoted 1 line

Does it make sense ?

Like I say I do think that merging your current code is better than nothing.

Great, thanks for bearing with me.

Thanks !
Lorenzo

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linaro-kernel at lists.linaro.org
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How we map non SMT (MT bit24=0) cores of dual/multi socket system with the topology which is using only aff0 and aff1?
can we use aff2 ( or concatenating aff2 and aff3) to represent socket-id?

thanks
Ganapat

Quoted 60 lines · Lorenzo Pieralisi

Quoted 23 lines · Mark Brown

Quoted 4 lines · Lorenzo Pieralisi

My question is: is it better to pack affinity levels and "guess" what aff3 (and aff2 on non-SMT) means or add an additional level of hierarchy in the arm64 topology code (eg book_id - implemented only for s390 to the best of my knowledge) ?

Shoving them in there would address the issue as well, yes (though we'd still have to combine aff2 and aff3 for the non-SMT case). I don't know if having books enabled has some overhead we don't want though.

Quoted 11 lines

I personally prefer the latter approach but I think it boils down to understanding what do we want to provide the scheduler with if we have a hierarchy that extends beyond "cluster" level.

I will be glad to help you implement it when time comes (and this will also fix the clusters of clusters DT issue we are facing - ie how to treat them).

Now, I do not think it is a major problem at the moment, merging the patch I sent will give us more time to discuss how to define the topology for clusters of clusters, because that's what we are talking about.

Quoted 12 lines

In so far as you're saying that we don't really need to worry about exactly how we handle multi-level clusters properly at the minute I agree with you - until we have some idea what they physically look like and can consider how well that maps onto the scheduler and whatnot it doesn't really matter and we can just ignore it. Given that I'm not concerned about just reporting everything as flat like we do with DT at the minute and don't see a real need to theorise about it, it'll just be a performance problem and not a correctness problem when it is encountered. That feels like a better position to leave things in as it will be less stress for whoever is bringing up such a fancy new system, they can stand a reasonable chance of getting things at least running with minimal effort.

Ok, I think we have an agreement, let's merge the patch I sent and discuss the way forward to cater for systems with clusters of clusters when we reasonably expect them to hit production, the scheduler expected topology might well change by that time and now we are well positioned to cope with future extensions (and actually packing affinity levels might well be the final solution if the scheduler expects a "flat" topology at the higher topology level).

Quoted 4 lines

Quoted 1 line

Does it make sense ?

Like I say I do think that merging your current code is better than nothing.

Great, thanks for bearing with me.

Thanks !
Lorenzo

_______________________________________________
linaro-kernel mailing list
linaro-kernel at lists.linaro.org
http://lists.linaro.org/mailman/listinfo/linaro-kernel

Quoted 3 lines · Ganapatrao Kulkarni

How we map non SMT (MT bit24=0) cores of dual/multi socket system with the topology which is using only aff0 and aff1?
can we use aff2 ( or concatenating aff2 and aff3) to represent socket-id?

Can you provide us with a description of the topology and the MPIDR_EL1 list please ?

I think that DT squashes the levels above cluster so that's how it could be implemented but first I would like to see what s the CPUs layout of the system.

Thanks,
Lorenzo

Quoted 68 lines

thanks
Ganapat

Quoted 60 lines · Lorenzo Pieralisi

Quoted 23 lines · Mark Brown

Quoted 4 lines · Lorenzo Pieralisi

My question is: is it better to pack affinity levels and "guess" what aff3 (and aff2 on non-SMT) means or add an additional level of hierarchy in the arm64 topology code (eg book_id - implemented only for s390 to the best of my knowledge) ?

Shoving them in there would address the issue as well, yes (though we'd still have to combine aff2 and aff3 for the non-SMT case). I don't know if having books enabled has some overhead we don't want though.

Quoted 11 lines

I personally prefer the latter approach but I think it boils down to understanding what do we want to provide the scheduler with if we have a hierarchy that extends beyond "cluster" level.

I will be glad to help you implement it when time comes (and this will also fix the clusters of clusters DT issue we are facing - ie how to treat them).

Now, I do not think it is a major problem at the moment, merging the patch I sent will give us more time to discuss how to define the topology for clusters of clusters, because that's what we are talking about.

Quoted 12 lines

In so far as you're saying that we don't really need to worry about exactly how we handle multi-level clusters properly at the minute I agree with you - until we have some idea what they physically look like and can consider how well that maps onto the scheduler and whatnot it doesn't really matter and we can just ignore it. Given that I'm not concerned about just reporting everything as flat like we do with DT at the minute and don't see a real need to theorise about it, it'll just be a performance problem and not a correctness problem when it is encountered. That feels like a better position to leave things in as it will be less stress for whoever is bringing up such a fancy new system, they can stand a reasonable chance of getting things at least running with minimal effort.

Ok, I think we have an agreement, let's merge the patch I sent and discuss the way forward to cater for systems with clusters of clusters when we reasonably expect them to hit production, the scheduler expected topology might well change by that time and now we are well positioned to cope with future extensions (and actually packing affinity levels might well be the final solution if the scheduler expects a "flat" topology at the higher topology level).

Quoted 4 lines

Quoted 1 line

Does it make sense ?

Like I say I do think that merging your current code is better than nothing.

Great, thanks for bearing with me.

Thanks !
Lorenzo

_______________________________________________
linaro-kernel mailing list
linaro-kernel at lists.linaro.org
http://lists.linaro.org/mailman/listinfo/linaro-kernel

Hi Lorenzo,

Quoted 11 lines · Lorenzo Pieralisi

Quoted 3 lines · Ganapatrao Kulkarni

How we map non SMT (MT bit24=0) cores of dual/multi socket system with the topology which is using only aff0 and aff1?
can we use aff2 ( or concatenating aff2 and aff3) to represent socket-id?

Can you provide us with a description of the topology and the MPIDR_EL1 list please ?

I think that DT squashes the levels above cluster so that's how it could be implemented but first I would like to see what s the CPUs layout of the system.

Our Soc has 48 core(Cavium's thunderX) design. 48 cores are sub-grouped in to 3 clusters.
In turn each cluster is having 16 cores.
We do have support for connecting 2 SoCs and making single system of 96 cores.

the MPIDR mapping for this topology is,

Aff0 is mapped to 16 cores within a cluster. Valid range is 0 to 0xf Aff1 is mapped to cluster number, valid values are 0,1 and 2. Aff2 is mapped to Socket-id or SoC number. Valid values are 0 and 1.

Hi Ganapatrao,

Quoted 21 lines · Ganapatrao Kulkarni

Hi Lorenzo,

Quoted 11 lines · Lorenzo Pieralisi

Quoted 3 lines · Ganapatrao Kulkarni

How we map non SMT (MT bit24=0) cores of dual/multi socket system with the topology which is using only aff0 and aff1?
can we use aff2 ( or concatenating aff2 and aff3) to represent socket-id?

Can you provide us with a description of the topology and the MPIDR_EL1 list please ?

I think that DT squashes the levels above cluster so that's how it could be implemented but first I would like to see what s the CPUs layout of the system.

Our Soc has 48 core(Cavium's thunderX) design. 48 cores are sub-grouped in to 3 clusters.
In turn each cluster is having 16 cores.
We do have support for connecting 2 SoCs and making single system of 96 cores.

Quoted 5 lines

the MPIDR mapping for this topology is,

Aff0 is mapped to 16 cores within a cluster. Valid range is 0 to 0xf Aff1 is mapped to cluster number, valid values are 0,1 and 2. Aff2 is mapped to Socket-id or SoC number. Valid values are 0 and 1.

So, we went back and forth a few times and finally settled on what's merged into 3.17, due to lack of visibility into hardware that'll be shipped.

At one point, we had something approximating behavior of DT-based topology, along the lines of:

        if (mpidr & MPIDR_MT_BITMASK) {
                /* Multiprocessor system : Multi-threads per core */
                cpuid_topo->thread_id  = MPIDR_AFFINITY_LEVEL(mpidr, 0);
                cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 1);
                cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 2) |
                                         MPIDR_AFFINITY_LEVEL(mpidr, 3) << 8;
        } else {
                /* Multiprocessor system : Single-thread per core */
                cpuid_topo->thread_id  = -1;
                cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
                cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 1) |
                                         MPIDR_AFFINITY_LEVEL(mpidr, 2) << 8 |
                                         MPIDR_AFFINITY_LEVEL(mpidr, 3) << 16;
        }

BTW, Mark Brown just posted "[PATCH] arm64: topology: Fix handling of multi-level cluster MPIDR-based detection" which reintroduces the above, albeit only for MT case.

I suspect you're looking for something above for the non-MT case? As a workaround, have you considered defining your topology in DT?

Lorenzo,

Are you open to the above "workaround" given that Thunder is facing the current deficiency for non-MT case?
Or is it time to introduce socket_id or something equivalent?

Quoted 62 lines · Zi Shen Lim

Hi Ganapatrao,

Quoted 21 lines · Ganapatrao Kulkarni

Hi Lorenzo,

Quoted 11 lines · Lorenzo Pieralisi

Quoted 3 lines · Ganapatrao Kulkarni

How we map non SMT (MT bit24=0) cores of dual/multi socket system with the topology which is using only aff0 and aff1?
can we use aff2 ( or concatenating aff2 and aff3) to represent socket-id?

Can you provide us with a description of the topology and the MPIDR_EL1 list please ?

I think that DT squashes the levels above cluster so that's how it could be implemented but first I would like to see what s the CPUs layout of the system.

Our Soc has 48 core(Cavium's thunderX) design. 48 cores are sub-grouped in to 3 clusters.
In turn each cluster is having 16 cores.
We do have support for connecting 2 SoCs and making single system of 96 cores.

Quoted 5 lines

the MPIDR mapping for this topology is,

Aff0 is mapped to 16 cores within a cluster. Valid range is 0 to 0xf Aff1 is mapped to cluster number, valid values are 0,1 and 2. Aff2 is mapped to Socket-id or SoC number. Valid values are 0 and 1.

So, we went back and forth a few times and finally settled on what's merged into 3.17, due to lack of visibility into hardware that'll be shipped.

At one point, we had something approximating behavior of DT-based topology, along the lines of:

        if (mpidr & MPIDR_MT_BITMASK) {
                /* Multiprocessor system : Multi-threads per core */
                cpuid_topo->thread_id  = MPIDR_AFFINITY_LEVEL(mpidr, 0);
                cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 1);
                cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 2) |
                                         MPIDR_AFFINITY_LEVEL(mpidr, 3) << 8;
        } else {
                /* Multiprocessor system : Single-thread per core */
                cpuid_topo->thread_id  = -1;
                cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
                cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 1) |
                                         MPIDR_AFFINITY_LEVEL(mpidr, 2) << 8 |
                                         MPIDR_AFFINITY_LEVEL(mpidr, 3) << 16;
        }

BTW, Mark Brown just posted "[PATCH] arm64: topology: Fix handling of multi-level cluster MPIDR-based detection" which reintroduces the above, albeit only for MT case.

I suspect you're looking for something above for the non-MT case? As a workaround, have you considered defining your topology in DT?

Lorenzo,

Quoted 3 lines

Are you open to the above "workaround" given that Thunder is facing the current deficiency for non-MT case?
Or is it time to introduce socket_id or something equivalent?

Well, we have to do something for certain, I think M. Brown's patch seems a reasonable solution to this problem, I will give it more thought and come back to you beginning of September (I am currently on holiday).

Thank you,
Lorenzo