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

arch/x86/include/asm/apic.h

+6 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/include/asm/topology.h

+3 −1
Original line number Diff line number Diff line
@@ -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)

arch/x86/kernel/apic/apic.c

+15 −0
Original line number Diff line number Diff line
@@ -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.

arch/x86/kernel/smpboot.c

+9 −0
Original line number Diff line number Diff line
@@ -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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