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Message-ID: <20241223163448.00004354@huawei.com>
Date: Mon, 23 Dec 2024 16:34:48 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Yicong Yang <yangyicong@...wei.com>
CC: <catalin.marinas@....com>, <will@...nel.org>, <sudeep.holla@....com>,
<tglx@...utronix.de>, <peterz@...radead.org>, <mpe@...erman.id.au>,
<linux-arm-kernel@...ts.infradead.org>, <mingo@...hat.com>, <bp@...en8.de>,
<dave.hansen@...ux.intel.com>, <pierre.gondois@....com>,
<dietmar.eggemann@....com>, <yangyicong@...ilicon.com>,
<linuxppc-dev@...ts.ozlabs.org>, <x86@...nel.org>,
<linux-kernel@...r.kernel.org>, <morten.rasmussen@....com>,
<msuchanek@...e.de>, <gregkh@...uxfoundation.org>, <rafael@...nel.org>,
<prime.zeng@...ilicon.com>, <linuxarm@...wei.com>, <xuwei5@...wei.com>,
<guohanjun@...wei.com>
Subject: Re: [PATCH v10 1/4] cpu/SMT: Provide a default
topology_is_primary_thread()
On Fri, 20 Dec 2024 15:59:27 +0800
Yicong Yang <yangyicong@...wei.com> wrote:
> On 2024/12/20 15:53, Yicong Yang wrote:
> > From: Yicong Yang <yangyicong@...ilicon.com>
> >
> > Currently if architectures want to support HOTPLUG_SMT they need to
> > provide a topology_is_primary_thread() telling the framework which
> > thread in the SMT cannot offline. However arm64 doesn't have a
> > restriction on which thread in the SMT cannot offline, a simplest
> > choice is that just make 1st thread as the "primary" thread. So
> > just make this as the default implementation in the framework and
> > let architectures like x86 that have special primary thread to
> > override this function (which they've already done).
> >
> > There's no need to provide a stub function if !CONFIG_SMP or
> > !CONFIG_HOTPLUG_SMP. In such case the testing CPU is already
> > the 1st CPU in the SMT so it's always the primary thread.
> >
> > Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> > ---
> > As questioned in v9 [1] whether this works on architectures not using
> > CONFIG_GENERIC_ARCH_TOPOLOGY, hacked on LoongArch VM and this also works.
> > Architectures should use this on their own situation.
> > [1] https://lore.kernel.org/linux-arm-kernel/427bd639-33c3-47e4-9e83-68c428eb1a7d@arm.com/
> >
> > [root@...alhost smt]# uname -m
> > loongarch64
> > [root@...alhost smt]# pwd
> > /sys/devices/system/cpu/smt
> > [root@...alhost smt]# cat ../possible
> > 0-3
> > [root@...alhost smt]# cat ../online
> > 0-3
> > [root@...alhost smt]# cat control
> > on
> > [root@...alhost smt]# echo off > control
> > [root@...alhost smt]# cat control
> > off
> > [root@...alhost smt]# cat ../online
> > 0,2
> > [root@...alhost smt]# echo on > control
> > [root@...alhost smt]# cat control
> > on
> > [root@...alhost smt]# cat ../online
> > 0-3
>
> Tested with below code using the topology_is_primary_thread() introduced
> in this patch. Tested on an ACPI-based QEMU VM emulating SMT2.
Nice bit of testing.
Given it all seems fine. FWIW
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
(for original patch, not the longarch one!)
>
> Subject: [PATCH] LoongArch: Support HOTPLUG_SMT on ACPI-based system
>
> Support HOTPLUG_SMT on ACPI-based system using generic
> topology_is_primary_thread().
>
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> ---
> arch/loongarch/Kconfig | 1 +
> arch/loongarch/kernel/acpi.c | 26 ++++++++++++++++++++++++--
> 2 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index dae3a9104ca6..bed1b0640b97 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -172,6 +172,7 @@ config LOONGARCH
> select HAVE_SYSCALL_TRACEPOINTS
> select HAVE_TIF_NOHZ
> select HAVE_VIRT_CPU_ACCOUNTING_GEN if !SMP
> + select HOTPLUG_SMT if HOTPLUG_CPU
> select IRQ_FORCED_THREADING
> select IRQ_LOONGARCH_CPU
> select LOCK_MM_AND_FIND_VMA
> diff --git a/arch/loongarch/kernel/acpi.c b/arch/loongarch/kernel/acpi.c
> index 382a09a7152c..e642b0de57e7 100644
> --- a/arch/loongarch/kernel/acpi.c
> +++ b/arch/loongarch/kernel/acpi.c
> @@ -15,9 +15,11 @@
> #include <linux/memblock.h>
> #include <linux/of_fdt.h>
> #include <linux/serial_core.h>
> +#include <linux/xarray.h>
> #include <asm/io.h>
> #include <asm/numa.h>
> #include <asm/loongson.h>
> +#include <linux/cpu_smt.h>
>
> int acpi_disabled;
> EXPORT_SYMBOL(acpi_disabled);
> @@ -175,8 +177,12 @@ int pptt_enabled;
>
> int __init parse_acpi_topology(void)
> {
> + int thread_num, max_smt_thread_num = 1;
> + struct xarray core_threads;
> int cpu, topology_id;
> + void *entry;
>
> + xa_init(&core_threads);
> for_each_possible_cpu(cpu) {
> topology_id = find_acpi_cpu_topology(cpu, 0);
> if (topology_id < 0) {
> @@ -184,19 +190,35 @@ int __init parse_acpi_topology(void)
> return -ENOENT;
> }
>
> - if (acpi_pptt_cpu_is_thread(cpu) <= 0)
> + if (acpi_pptt_cpu_is_thread(cpu) <= 0) {
> cpu_data[cpu].core = topology_id;
> - else {
> + } else {
> topology_id = find_acpi_cpu_topology(cpu, 1);
> if (topology_id < 0)
> return -ENOENT;
>
> cpu_data[cpu].core = topology_id;
> +
> + entry = xa_load(&core_threads, topology_id);
> + if (!entry) {
> + xa_store(&core_threads, topology_id,
> + xa_mk_value(1), GFP_KERNEL);
> + } else {
> + thread_num = xa_to_value(entry);
> + thread_num++;
> + xa_store(&core_threads, topology_id,
> + xa_mk_value(thread_num), GFP_KERNEL);
> +
> + if (thread_num > max_smt_thread_num)
> + max_smt_thread_num = thread_num;
> + }
> }
> }
>
> pptt_enabled = 1;
>
> + cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
> + xa_destroy(&core_threads);
> return 0;
> }
>
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