Re: [PATCH v6 11/12] arm64: topology: enable ACPI/PPTT based CPU topology

[Xiongfeng Wang <wangxiongfeng2@huawei.com>]

Hi Jeremy,

I have tested the patch with the newest UEFI. It prints the below error:

[    4.017371] BUG: arch topology borken
[    4.021069] BUG: arch topology borken
[    4.024764] BUG: arch topology borken
[    4.028460] BUG: arch topology borken
[    4.032153] BUG: arch topology borken
[    4.035849] BUG: arch topology borken
[    4.039543] BUG: arch topology borken
[    4.043239] BUG: arch topology borken
[    4.046932] BUG: arch topology borken
[    4.050629] BUG: arch topology borken
[    4.054322] BUG: arch topology borken

I checked the code and found that the newest UEFI set PPTT physical_package_flag on a physical package node and
the NUMA domain (SRAT domains) starts from the layer of DIE. (The topology of our board is core->cluster->die->package).

When the kernel starts to build sched_domain, the multi-core sched_domain contains all the cores within a package,
and the lowest NUMA sched_domain contains all the cores within a die. But the kernel requires that the multi-core
sched_domain should be a subset of the lowest NUMA sched_domain, so the BUG info is printed.

If we modify the UEFI to make NUMA sched_domain start from the layer of package, then all the topology information
within the package will be discarded. I think we need to build the multi-core sched_domain using the cores within
the cluster instead of the cores within the package. I think that's what 'multi-core' means. Multi cores form a cluster. I guess.
If we build the multi-core sched_domain using the cores within a cluster, I think we need to add fields in struct cpu_topology
to record which cores are in each cluster.


Thanks,
Xiongfeng

On 2018/1/13 8:59, Jeremy Linton wrote:
> Propagate the topology information from the PPTT tree to the
> cpu_topology array. We can get the thread id, core_id and
> cluster_id by assuming certain levels of the PPTT tree correspond
> to those concepts. The package_id is flagged in the tree and can be
> found by calling find_acpi_cpu_topology_package() which terminates
> its search when it finds an ACPI node flagged as the physical
> package. If the tree doesn't contain enough levels to represent
> all of the requested levels then the root node will be returned
> for all subsequent levels.
> 
> Cc: Juri Lelli <juri.lelli@arm.com>
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  arch/arm64/kernel/topology.c | 46 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 7b06e263fdd1..ce8ec7fd6b32 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -11,6 +11,7 @@
>   * for more details.
>   */
>  
> +#include <linux/acpi.h>
>  #include <linux/arch_topology.h>
>  #include <linux/cpu.h>
>  #include <linux/cpumask.h>
> @@ -22,6 +23,7 @@
>  #include <linux/sched.h>
>  #include <linux/sched/topology.h>
>  #include <linux/slab.h>
> +#include <linux/smp.h>
>  #include <linux/string.h>
>  
>  #include <asm/cpu.h>
> @@ -300,6 +302,46 @@ static void __init reset_cpu_topology(void)
>  	}
>  }
>  
> +#ifdef CONFIG_ACPI
> +/*
> + * 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) {
> +		topology_id = find_acpi_cpu_topology(cpu, 0);
> +		if (topology_id < 0)
> +			return topology_id;
> +
> +		if (is_threaded) {
> +			cpu_topology[cpu].thread_id = topology_id;
> +			topology_id = find_acpi_cpu_topology(cpu, 1);
> +			cpu_topology[cpu].core_id   = topology_id;
> +			topology_id = find_acpi_cpu_topology_package(cpu);
> +			cpu_topology[cpu].package_id = topology_id;
> +		} else {
> +			cpu_topology[cpu].thread_id  = -1;
> +			cpu_topology[cpu].core_id    = topology_id;
> +			topology_id = find_acpi_cpu_topology_package(cpu);
> +			cpu_topology[cpu].package_id = topology_id;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +#else
> +static inline int __init parse_acpi_topology(void)
> +{
> +	return -EINVAL;
> +}
> +#endif
>  
>  void __init init_cpu_topology(void)
>  {
> @@ -309,6 +351,8 @@ void __init init_cpu_topology(void)
>  	 * Discard anything that was parsed if we hit an error so we
>  	 * don't use partial information.
>  	 */
> -	if (of_have_populated_dt() && parse_dt_topology())
> +	if ((!acpi_disabled) && parse_acpi_topology())
> +		reset_cpu_topology();
> +	else if (of_have_populated_dt() && parse_dt_topology())
>  		reset_cpu_topology();
>  }
>