Commit 6a4d2657 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

x86/smp: Provide topology_is_primary_thread()



If the CPU is supporting SMT then the primary thread can be found by
checking the lower APIC ID bits for zero. smp_num_siblings is used to build
the mask for the APIC ID bits which need to be taken into account.

This uses the MPTABLE or ACPI/MADT supplied APIC ID, which can be different
than the initial APIC ID in CPUID. But according to AMD the lower bits have
to be consistent. Intel gave a tentative confirmation as well.

Preparatory patch to support disabling SMT at boot/runtime.
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
parent ba2591a5
......@@ -502,6 +502,12 @@ extern int default_check_phys_apicid_present(int phys_apicid);
#endif /* CONFIG_X86_LOCAL_APIC */
#ifdef CONFIG_SMP
bool apic_id_is_primary_thread(unsigned int id);
#else
static inline bool apic_id_is_primary_thread(unsigned int id) { return false; }
#endif
extern void irq_enter(void);
extern void irq_exit(void);
......
......@@ -123,13 +123,15 @@ static inline int topology_max_smt_threads(void)
}
int topology_update_package_map(unsigned int apicid, unsigned int cpu);
extern int topology_phys_to_logical_pkg(unsigned int pkg);
int topology_phys_to_logical_pkg(unsigned int pkg);
bool topology_is_primary_thread(unsigned int cpu);
#else
#define topology_max_packages() (1)
static inline int
topology_update_package_map(unsigned int apicid, unsigned int cpu) { return 0; }
static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return 0; }
static inline int topology_max_smt_threads(void) { return 1; }
static inline bool topology_is_primary_thread(unsigned int cpu) { return true; }
#endif
static inline void arch_fix_phys_package_id(int num, u32 slot)
......
......@@ -2189,6 +2189,21 @@ static int cpuid_to_apicid[] = {
[0 ... NR_CPUS - 1] = -1,
};
/**
* apic_id_is_primary_thread - Check whether APIC ID belongs to a primary thread
* @id: APIC ID to check
*/
bool apic_id_is_primary_thread(unsigned int apicid)
{
u32 mask;
if (smp_num_siblings == 1)
return true;
/* Isolate the SMT bit(s) in the APICID and check for 0 */
mask = (1U << (fls(smp_num_siblings) - 1)) - 1;
return !(apicid & mask);
}
/*
* Should use this API to allocate logical CPU IDs to keep nr_logical_cpuids
* and cpuid_to_apicid[] synchronized.
......
......@@ -265,6 +265,15 @@ static void notrace start_secondary(void *unused)
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
}
/**
* topology_is_primary_thread - Check whether CPU is the primary SMT thread
* @cpu: CPU to check
*/
bool topology_is_primary_thread(unsigned int cpu)
{
return apic_id_is_primary_thread(per_cpu(x86_cpu_to_apicid, cpu));
}
/**
* topology_phys_to_logical_pkg - Map a physical package id to a logical
*
......
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