[SPARC64]: Add SMT scheduling support for Niagara.

The mapping is a simple "(cpuid >> 2) == core" for now.
Later we'll add more sophisticated code that will walk
the sun4v machine description and figure this out from
there.

We should also add core mappings for jaguar and panther
processors.

Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/Kconfig

@@ -356,6 +356,15 @@ config SOLARIS_EMUL
 
 endmenu
 
+config SCHED_SMT
+	bool "SMT (Hyperthreading) scheduler support"
+	depends on SMP
+	default y
+	help
+	  SMT scheduler support improves the CPU scheduler's decision making
+	  when dealing with UltraSPARC cpus at a cost of slightly increased
+	  overhead in some places. If unsure say N here.
+
 config CMDLINE_BOOL
 	bool "Default bootloader kernel arguments"
 

arch/sparc64/kernel/smp.c

@@ -47,6 +47,8 @@ static unsigned char boot_cpu_id;
 
 cpumask_t cpu_online_map __read_mostly = CPU_MASK_NONE;
 cpumask_t phys_cpu_present_map __read_mostly = CPU_MASK_NONE;
+cpumask_t cpu_sibling_map[NR_CPUS] __read_mostly =
+	{ [0 ... NR_CPUS-1] = CPU_MASK_NONE };
 static cpumask_t smp_commenced_mask;
 static cpumask_t cpu_callout_map;
 
@@ -1291,6 +1293,8 @@ int setup_profiling_timer(unsigned int multiplier)
 /* Constrain the number of cpus to max_cpus.  */
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
+	int i;
+
 	if (num_possible_cpus() > max_cpus) {
 		int instance, mid;
 
@@ -1305,6 +1309,20 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 		}
 	}
 
+	for_each_cpu(i) {
+		if (tlb_type == hypervisor) {
+			int j;
+
+			/* XXX get this mapping from machine description */
+			for_each_cpu(j) {
+				if ((j >> 2) == (i >> 2))
+					cpu_set(j, cpu_sibling_map[i]);
+			}
+		} else {
+			cpu_set(i, cpu_sibling_map[i]);
+		}
+	}
+
 	smp_store_cpu_info(boot_cpu_id);
 }
 

include/asm-sparc64/smp.h

@@ -33,6 +33,8 @@
 extern cpumask_t phys_cpu_present_map;
 #define cpu_possible_map phys_cpu_present_map
 
+extern cpumask_t cpu_sibling_map[NR_CPUS];
+
 /*
  *	General functions that each host system must provide.
  */