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Message-ID: <CAEEQ3wmbHuyVMpiU_zaxjgS-Tm8Ve=rDVLgY7qoA-ZBZjx_hJg@mail.gmail.com>
Date: Thu, 18 Sep 2025 09:24:23 +0800
From: yunhui cui <cuiyunhui@...edance.com>
To: Yicong Yang <yangyicong@...wei.com>
Cc: catalin.marinas@....com, will@...nel.org, sudeep.holla@....com,
gregkh@...uxfoundation.org, rafael@...nel.org, dakr@...nel.org,
beata.michalska@....com, sumitg@...dia.com, ptsm@...ux.microsoft.com,
yangyicong@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] arch_topology: move parse_acpi_topology()
to common code
Hi Yicong,
On Wed, Sep 17, 2025 at 2:43 PM Yicong Yang <yangyicong@...wei.com> wrote:
>
> On 2025/9/17 10:30, Yunhui Cui wrote:
> > Currently, RISC-V lacks arch-specific registers for CPU topology
> > properties and must get them from ACPI. Thus, parse_acpi_topology()
> > is moved from arm64/ to drivers/ for RISC-V reuse.
> >
> > Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> > ---
> > arch/arm64/kernel/topology.c | 87 +----------------------------------
> > drivers/base/arch_topology.c | 85 +++++++++++++++++++++++++++++++++-
> > include/linux/arch_topology.h | 6 +++
> > 3 files changed, 91 insertions(+), 87 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > index 5d07ee85bdae4..55650db53b526 100644
> > --- a/arch/arm64/kernel/topology.c
> > +++ b/arch/arm64/kernel/topology.c
> > @@ -26,7 +26,7 @@
> > #include <asm/topology.h>
> >
> > #ifdef CONFIG_ACPI
> > -static bool __init acpi_cpu_is_threaded(int cpu)
> > +bool __init acpi_cpu_is_threaded(int cpu)
> > {
> > int is_threaded = acpi_pptt_cpu_is_thread(cpu);
> >
> > @@ -39,91 +39,6 @@ static bool __init acpi_cpu_is_threaded(int cpu)
> >
> > return !!is_threaded;
> > }
> > -
> > -struct cpu_smt_info {
> > - unsigned int thread_num;
> > - int core_id;
> > -};
> > -
> > -/*
> > - * Propagate the topology information of the processor_topology_node tree to the
> > - * cpu_topology array.
> > - */
> > -int __init parse_acpi_topology(void)
> > -{
> > - unsigned int max_smt_thread_num = 1;
> > - struct cpu_smt_info *entry;
> > - struct xarray hetero_cpu;
> > - unsigned long hetero_id;
> > - int cpu, topology_id;
> > -
> > - if (acpi_disabled)
> > - return 0;
> > -
> > - xa_init(&hetero_cpu);
> > -
> > - for_each_possible_cpu(cpu) {
> > - topology_id = find_acpi_cpu_topology(cpu, 0);
> > - if (topology_id < 0)
> > - return topology_id;
> > -
> > - 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;
> > -
> > - /*
> > - * In the PPTT, CPUs below a node with the 'identical
> > - * implementation' flag have the same number of threads.
> > - * Count the number of threads for only one CPU (i.e.
> > - * one core_id) among those with the same hetero_id.
> > - * See the comment of find_acpi_cpu_topology_hetero_id()
> > - * for more details.
> > - *
> > - * One entry is created for each node having:
> > - * - the 'identical implementation' flag
> > - * - its parent not having the flag
> > - */
> > - hetero_id = find_acpi_cpu_topology_hetero_id(cpu);
> > - entry = xa_load(&hetero_cpu, hetero_id);
> > - if (!entry) {
> > - entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > - WARN_ON_ONCE(!entry);
> > -
> > - if (entry) {
> > - entry->core_id = topology_id;
> > - entry->thread_num = 1;
> > - xa_store(&hetero_cpu, hetero_id,
> > - entry, GFP_KERNEL);
> > - }
> > - } else if (entry->core_id == topology_id) {
> > - entry->thread_num++;
> > - }
> > - } else {
> > - cpu_topology[cpu].thread_id = -1;
> > - cpu_topology[cpu].core_id = topology_id;
> > - }
> > - topology_id = find_acpi_cpu_topology_cluster(cpu);
> > - cpu_topology[cpu].cluster_id = topology_id;
> > - topology_id = find_acpi_cpu_topology_package(cpu);
> > - cpu_topology[cpu].package_id = topology_id;
> > - }
> > -
> > - /*
> > - * This is a short loop since the number of XArray elements is the
> > - * number of heterogeneous CPU clusters. On a homogeneous system
> > - * there's only one entry in the XArray.
> > - */
> > - xa_for_each(&hetero_cpu, hetero_id, entry) {
> > - max_smt_thread_num = max(max_smt_thread_num, entry->thread_num);
> > - xa_erase(&hetero_cpu, hetero_id);
> > - kfree(entry);
> > - }
> > -
> > - cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
> > - xa_destroy(&hetero_cpu);
> > - return 0;
> > -}
> > #endif
> >
> > #ifdef CONFIG_ARM64_AMU_EXTN
> > diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> > index 1037169abb459..65ec1f3d2bd28 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -823,12 +823,95 @@ void remove_cpu_topology(unsigned int cpu)
> > clear_cpu_topology(cpu);
> > }
> >
> > +__weak bool __init acpi_cpu_is_threaded(int cpu)
> > +{
> > + int is_threaded = acpi_pptt_cpu_is_thread(cpu);
> > +
> > + return !!is_threaded;
> > +
>
> acpi_pptt_cpu_is_thread() could return an error which shouldn't be
> regarded as a threaded cpu.
>
> > +}
> > +
> > +#if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
> > +/*
> > + * Propagate the topology information of the processor_topology_node tree to the
> > + * cpu_topology array.
> > + */
> > __weak int __init parse_acpi_topology(void)
> > {
> > + unsigned int max_smt_thread_num = 1;
> > + struct cpu_smt_info *entry;
> > + struct xarray hetero_cpu;
> > + unsigned long hetero_id;
> > + int cpu, topology_id;
> > +
> > + if (acpi_disabled)
> > + return 0;
> > +
> > + xa_init(&hetero_cpu);
> > +
> > + for_each_possible_cpu(cpu) {
> > + topology_id = find_acpi_cpu_topology(cpu, 0);
> > + if (topology_id < 0)
> > + return topology_id;
> > +
> > + 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;
> > +
> > + /*
> > + * In the PPTT, CPUs below a node with the 'identical
> > + * implementation' flag have the same number of threads.
> > + * Count the number of threads for only one CPU (i.e.
> > + * one core_id) among those with the same hetero_id.
> > + * See the comment of find_acpi_cpu_topology_hetero_id()
> > + * for more details.
> > + *
> > + * One entry is created for each node having:
> > + * - the 'identical implementation' flag
> > + * - its parent not having the flag
> > + */
> > + hetero_id = find_acpi_cpu_topology_hetero_id(cpu);
> > + entry = xa_load(&hetero_cpu, hetero_id);
> > + if (!entry) {
> > + entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > + WARN_ON_ONCE(!entry);
> > +
> > + if (entry) {
> > + entry->core_id = topology_id;
> > + entry->thread_num = 1;
> > + xa_store(&hetero_cpu, hetero_id,
> > + entry, GFP_KERNEL);
> > + }
> > + } else if (entry->core_id == topology_id) {
> > + entry->thread_num++;
> > + }
> > + } else {
> > + cpu_topology[cpu].thread_id = -1;
> > + cpu_topology[cpu].core_id = topology_id;
> > + }
> > + topology_id = find_acpi_cpu_topology_cluster(cpu);
> > + cpu_topology[cpu].cluster_id = topology_id;
> > + topology_id = find_acpi_cpu_topology_package(cpu);
> > + cpu_topology[cpu].package_id = topology_id;
> > + }
> > +
> > + /*
> > + * This is a short loop since the number of XArray elements is the
> > + * number of heterogeneous CPU clusters. On a homogeneous system
> > + * there's only one entry in the XArray.
> > + */
> > + xa_for_each(&hetero_cpu, hetero_id, entry) {
> > + max_smt_thread_num = max(max_smt_thread_num, entry->thread_num);
> > + xa_erase(&hetero_cpu, hetero_id);
> > + kfree(entry);
> > + }
> > +
> > + cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
> > + xa_destroy(&hetero_cpu);
> > return 0;
> > }
> >
> > -#if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
> > void __init init_cpu_topology(void)
> > {
> > int cpu, ret;
> > diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> > index d72d6e5aa2002..50d33b5a78ccd 100644
> > --- a/include/linux/arch_topology.h
> > +++ b/include/linux/arch_topology.h
> > @@ -70,6 +70,11 @@ struct cpu_topology {
> > cpumask_t llc_sibling;
> > };
> >
> > +struct cpu_smt_info {
> > + unsigned int thread_num;
> > + int core_id;
> > +};
> > +
>
> this is only used in parse_acpi_topology() and seems no reason to make it into
> the header.
Okay, I'll update it in v2.
>
> otherwise looks good to me. most acpi topology building code is not arm64
> specific and make sense to make it common.
>
> thanks.
>
Thanks,
Yunhui
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