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x86/smp: Add a per-cpu view of SMT state 

A new field smt_active in cpuinfo_x86 identifies if the current core/cpu
is in SMT mode or not.

This is helpful when the system has some of its cores with threads offlined
and can be used for cases where action is taken based on the state of SMT.

The upcoming support for paranoid L1D flush will make use of this information.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Balbir Singh <sblbir@amazon.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210108121056.21940-2-sblbir@amazon.com
This commit is contained in:
Balbir Singh 2021-01-08 23:10:52 +11:00 committed by Thomas Gleixner
parent ff1176468d
commit c52787b590
2 changed files with 11 additions and 1 deletions
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2
arch/x86/include/asm/processor.h
View File

@ -136,6 +136,8 @@ struct cpuinfo_x86 {
u16 logical_die_id;
/* Index into per_cpu list: */
u16 cpu_index;
/* Is SMT active on this core? */
bool smt_active;
u32 microcode;
/* Address space bits used by the cache internally */
u8 x86_cache_bits;

10
arch/x86/kernel/smpboot.c
View File

@ -610,6 +610,9 @@ void set_cpu_sibling_map(int cpu)
if (threads > __max_smt_threads)
__max_smt_threads = threads;
for_each_cpu(i, topology_sibling_cpumask(cpu))
cpu_data(i).smt_active = threads > 1;
/*
* This needs a separate iteration over the cpus because we rely on all
* topology_sibling_cpumask links to be set-up.
@ -1552,8 +1555,13 @@ static void remove_siblinginfo(int cpu)
for_each_cpu(sibling, topology_die_cpumask(cpu))
cpumask_clear_cpu(cpu, topology_die_cpumask(sibling));
for_each_cpu(sibling, topology_sibling_cpumask(cpu))
for_each_cpu(sibling, topology_sibling_cpumask(cpu)) {
cpumask_clear_cpu(cpu, topology_sibling_cpumask(sibling));
if (cpumask_weight(topology_sibling_cpumask(sibling)) == 1)
cpu_data(sibling).smt_active = false;
}
for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
cpumask_clear(cpu_llc_shared_mask(cpu));