x86/topology: Add topology_max_smt_threads()

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.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Cc: jolsa@kernel.org
Link: http://lkml.kernel.org/r/1463703002-19686-2-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 24 insertions, 1 deletions

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index fafe8b923cac..2ed0ec1353f8 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;
@@ -493,7 +496,7 @@ 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);
 
@@ -550,6 +553,10 @@ 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 */
@@ -1441,6 +1448,21 @@ __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;
@@ -1465,6 +1487,7 @@ 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)