[UPDATED PATCH 01/10] x86: Add topology_max_smt_threads()

[Andi Kleen]

For SMT specific workarounds it is useful to know if SMT is active
on any online CPU in the system. This currently requires a loop
over all online CPUs.
    
Add a global variable that is updated with the maximum number
of smt threads on any CPU on online/offline, and use it for
topology_max_smt_threads()
    
The single call is easier to use than a loop.
    
Not exported to user space because user space already can use
the existing sibling interfaces to find this out.
    
v2: Code formatting changes and use __ for variable name
Cc: t...@linutronix.de
Signed-off-by: Andi Kleen <a...@linux.intel.com>

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index 7f991bd5031b..f79181c03561 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -129,6 +129,10 @@ extern const struct cpumask *cpu_coregroup_mask(int cpu);
 
 extern unsigned int __max_logical_packages;
 #define topology_max_packages()                        (__max_logical_packages)
+
+extern int __max_smt_threads;
+#define topology_max_smt_threads()             __max_smt_threads
+
 int topology_update_package_map(unsigned int apicid, unsigned int cpu);
 extern int topology_phys_to_logical_pkg(unsigned int pkg);
 #else
@@ -136,6 +140,7 @@ extern int topology_phys_to_logical_pkg(unsigned int pkg);
 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; }
+#define topology_max_smt_threads()             1
 #endif
 
 static inline void arch_fix_phys_package_id(int num, u32 slot)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index a2065d3b3b39..76bf9d855ee3 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -105,6 +105,9 @@ static unsigned int max_physical_pkg_id __read_mostly;
 unsigned int __max_logical_packages __read_mostly;
 EXPORT_SYMBOL(__max_logical_packages);
 
+/* Maximum number of SMT threads on any online core */
+int __max_smt_threads __read_mostly;
+
 static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 {
        unsigned long flags;
@@ -488,7 +491,7 @@ void set_cpu_sibling_map(int cpu)
        bool has_mp = has_smt || boot_cpu_data.x86_max_cores > 1;
        struct cpuinfo_x86 *c = &cpu_data(cpu);
        struct cpuinfo_x86 *o;
-       int i;
+       int i, threads;
 
        cpumask_set_cpu(cpu, cpu_sibling_setup_mask);
 
@@ -545,6 +548,10 @@ void set_cpu_sibling_map(int cpu)
                if (match_die(c, o) && !topology_same_node(c, o))
                        primarily_use_numa_for_topology();
        }
+
+       threads = cpumask_weight(topology_sibling_cpumask(cpu));
+       if (threads > __max_smt_threads)
+               __max_smt_threads = threads;
 }
 
 /* maps the cpu to the sched domain representing multi-core */
@@ -1436,6 +1443,21 @@ __init void prefill_possible_map(void)
 
 #ifdef CONFIG_HOTPLUG_CPU
 
+/* Recompute SMT state for all CPUs on offline */
+static void recompute_smt_state(void)
+{
+       int max_threads, cpu;
+
+       max_threads = 0;
+       for_each_online_cpu (cpu) {
+               int threads = cpumask_weight(topology_sibling_cpumask(cpu));
+
+               if (threads > max_threads)
+                       max_threads = threads;
+       }
+       __max_smt_threads = max_threads;
+}
+
 static void remove_siblinginfo(int cpu)
 {
        int sibling;
@@ -1460,6 +1482,7 @@ static void remove_siblinginfo(int cpu)
        c->phys_proc_id = 0;
        c->cpu_core_id = 0;
        cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
+       recompute_smt_state();
 }
 
 static void remove_cpu_from_maps(int cpu)