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Message-ID: <CAEEQ3wkRoX5Y5xQu22kVCFxEy8fgcUxKHEm=9Bpg7g-Np8b-SA@mail.gmail.com>
Date: Mon, 22 Sep 2025 10:18:57 +0800
From: yunhui cui <cuiyunhui@...edance.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: catalin.marinas@....com, will@...nel.org, gregkh@...uxfoundation.org,
rafael@...nel.org, dakr@...nel.org, beata.michalska@....com,
ptsm@...ux.microsoft.com, sumitg@...dia.com, yangyicong@...ilicon.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v3 1/1] arch_topology: move
parse_acpi_topology() to common code
Hi Sudeep,
On Fri, Sep 19, 2025 at 10:05 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Fri, Sep 19, 2025 at 04:59:18PM +0800, 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 | 89 ++++++++++++++++++++++++++++++++++-
> > include/linux/arch_topology.h | 1 +
> > 3 files changed, 90 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..09f77fd549490 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -823,12 +823,99 @@ 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);
> > +
>
> Just thinking if it makes sense keep acpi_cpu_is_threaded generic without
> the need for weak definition.
>
> Additional note: not sure why you haven't moved this under CONFIG_ARM64/RISCV as
> done with other code.
>
> bool __init acpi_cpu_is_threaded(int cpu)
> {
> int is_threaded = acpi_pptt_cpu_is_thread(cpu);
>
> /*
> * if the PPTT doesn't have thread information, check for architecture
> * specific fallback if available
> */
> if (is_threaded < 0)
> is_threaded = arch_cpu_is_threaded();
>
> return !!is_threaded;
> }
>
> Then you can just have the define in
>
> #define arch_cpu_is_threaded() (read_cpuid_mpidr() & MPIDR_MT_BITMASK)
>
> in arch/arm64/include/asm/topology.h
>
> and
>
> +#ifndef arch_cpu_is_threaded
> +#define arch_cpu_is_threaded (0)
> +#endif
>
> in include/linux/arch_topology.h
>
> Thoughts ?
If placed in include/linux/arch_topology.h, there is a possibility
that "arch_cpu_is_threaded" will be redefined.
include/linux/topology.h
#include <linux/arch_topology.h>
#ifndef arch_cpu_is_threaded
#define arch_cpu_is_threaded() (0)
#endif
#include <asm/topology.h>
#define arch_cpu_is_threaded() (read_cpuid_mpidr() & MPIDR_MT_BITMASK)
Therefore, it is better to place it in include/asm-generic/topology.h.
What do you think?
>
> --
> Regards,
> Sudeep
Thanks,
Yunhui
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