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powerpc: Add HOTPLUG_SMT support

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Add support for HOTPLUG_SMT, which enables the generic sysfs SMT support
files in /sys/devices/system/cpu/smt, as well as the "nosmt" boot
parameter.

Implement the recently added hooks to allow partial SMT states, allow
any number of threads per core.

Tie the config symbol to HOTPLUG_CPU, which enables it on the major
platforms that support SMT. If there are other platforms that want the
SMT support that can be tweaked in future.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[ldufour: remove topology_smt_supported]
[ldufour: remove topology_smt_threads_supported]
[ldufour: select CONFIG_SMT_NUM_THREADS_DYNAMIC]
[ldufour: update kernel-parameters.txt]
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Link: https://msgid.link/20230705145143.40545-10-ldufour@linux.ibm.com
This commit is contained in:
Michael Ellerman 2023-07-05 16:51:42 +02:00
parent 3b3a4d0fe5
commit 73c58e7e14
4 changed files with 26 additions and 3 deletions
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4
Documentation/admin-guide/kernel-parameters.txt
View file

@ -3853,10 +3853,10 @@
nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
and disable the IO APIC. legacy for "maxcpus=0".
nosmt [KNL,MIPS,S390] Disable symmetric multithreading (SMT).
nosmt [KNL,MIPS,PPC,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
[KNL,X86] Disable symmetric multithreading (SMT).
[KNL,X86,PPC] Disable symmetric multithreading (SMT).
nosmt=force: Force disable SMT, cannot be undone
via the sysfs control file.

2
arch/powerpc/Kconfig
View file

@ -272,6 +272,8 @@ config PPC
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_VIRT_CPU_ACCOUNTING
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select HOTPLUG_SMT if HOTPLUG_CPU
select SMT_NUM_THREADS_DYNAMIC
select HUGETLB_PAGE_SIZE_VARIABLE if PPC_BOOK3S_64 && HUGETLB_PAGE
select IOMMU_HELPER if PPC64
select IRQ_DOMAIN

15
arch/powerpc/include/asm/topology.h
View file

@ -143,5 +143,20 @@ static inline int cpu_to_coregroup_id(int cpu)
#endif
#endif
#ifdef CONFIG_HOTPLUG_SMT
#include <linux/cpu_smt.h>
#include <asm/cputhreads.h>
static inline bool topology_is_primary_thread(unsigned int cpu)
{
return cpu == cpu_first_thread_sibling(cpu);
}
static inline bool topology_smt_thread_allowed(unsigned int cpu)
{
return cpu_thread_in_core(cpu) < cpu_smt_num_threads;
}
#endif
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_TOPOLOGY_H */

8
arch/powerpc/kernel/smp.c
View file

@ -1087,7 +1087,7 @@ static int __init init_big_cores(void)
void __init smp_prepare_cpus(unsigned int max_cpus)
{
unsigned int cpu;
unsigned int cpu, num_threads;
DBG("smp_prepare_cpus\n");
@ -1154,6 +1154,12 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
if (smp_ops && smp_ops->probe)
smp_ops->probe();
// Initalise the generic SMT topology support
num_threads = 1;
if (smt_enabled_at_boot)
num_threads = smt_enabled_at_boot;
cpu_smt_set_num_threads(num_threads, threads_per_core);
}
void smp_prepare_boot_cpu(void)