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LoongArch: Add HOTPLUG_SMT implementation

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For benchmarking or debugging purpose, we usually want to control SMT
via boot parameter and sysfs knobs. So add HOTPLUG_SMT implementation.

1. Boot parameters:

nosmt:		Disable SMT, can be enabled via sysfs knobs.
nosmt=force:	Disable SMT, cannot be enabled via sysfs knobs.

2. Runtime sysfs controls:

Write "on", "off", "forceoff" or the number of SMT threads (1, 2, ...)
to /sys/devices/system/cpu/smt/control.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Huacai Chen 2026-02-10 19:31:13 +08:00
parent 94b0c831ed
commit 009ee0c964
3 changed files with 15 additions and 1 deletions
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2
Documentation/admin-guide/kernel-parameters.txt
View file

@ -4585,7 +4585,7 @@ Kernel parameters
nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
[KNL,X86,PPC,S390] Disable symmetric multithreading (SMT).
[KNL,LOONGARCH,X86,PPC,S390] Disable symmetric multithreading (SMT).
nosmt=force: Force disable SMT, cannot be undone
via the sysfs control file.

1
arch/loongarch/Kconfig
View file

@ -186,6 +186,7 @@ config LOONGARCH
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_TIF_NOHZ
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select HOTPLUG_SMT if HOTPLUG_CPU
select IRQ_FORCED_THREADING
select IRQ_LOONGARCH_CPU
select LOCK_MM_AND_FIND_VMA

13
arch/loongarch/kernel/smp.c
View file

@ -365,16 +365,29 @@ void __init loongson_smp_setup(void)
void __init loongson_prepare_cpus(unsigned int max_cpus)
{
int i = 0;
int threads_per_core = 0;
parse_acpi_topology();
cpu_data[0].global_id = cpu_logical_map(0);
if (!pptt_enabled)
threads_per_core = 1;
else {
for_each_possible_cpu(i) {
if (cpu_to_node(i) != 0)
continue;
if (cpus_are_siblings(0, i))
threads_per_core++;
}
}
for (i = 0; i < loongson_sysconf.nr_cpus; i++) {
set_cpu_present(i, true);
csr_mail_send(0, __cpu_logical_map[i], 0);
}
per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
cpu_smt_set_num_threads(threads_per_core, threads_per_core);
}
/*