[PATCH] Create cpu_sibling_map for PPC64

[Matthew Dobson]

In light of some proposed changes in the sched_domains code, I coded up
this little ditty that simply creates and populates a cpu_sibling_map
for PPC64 machines.  The patch just checks the CPU flags to determine if
the CPU supports SMT (aka Hyper-Threading aka Multi-Threading aka ...)
and fills in a mask of the siblings for each CPU in the system.  This
should allow us to build sched_domains for PPC64 with generic code in
kernel/sched.c for the SMT systems.  SMT is becoming more popular and is
turning up in more and more architectures.  I don't think it will be too
long until this feature is supported by most arches...

[mcd@arrakis source]$ diffstat
~/linux/patches/ppc64-cpu_sibling_map.patch
 arch/ppc64/kernel/smp.c |    7 +++++++
 include/asm-ppc64/smp.h |    1 +
 2 files changed, 8 insertions(+)

Signed-off-by: Matthew Dobson <colpatch@xxxxxxxxxx>

-Matt


diff -Nurp --exclude-from=/home/mcd/.dontdiff linux-2.6.8-rc2-mm1/arch/ppc64/kernel/smp.c linux-2.6.8-rc2-mm1+ppc64-cpu_sibling_map/arch/ppc64/kernel/smp.c
--- linux-2.6.8-rc2-mm1/arch/ppc64/kernel/smp.c	2004-07-28 10:50:29.000000000 -0700
+++ linux-2.6.8-rc2-mm1+ppc64-cpu_sibling_map/arch/ppc64/kernel/smp.c	2004-07-28 12:02:38.000000000 -0700
@@ -64,6 +64,7 @@ cpumask_t cpu_possible_map = CPU_MASK_NO
 cpumask_t cpu_online_map = CPU_MASK_NONE;
 cpumask_t cpu_available_map = CPU_MASK_NONE;
 cpumask_t cpu_present_at_boot = CPU_MASK_NONE;
+cpumask_t cpu_sibling_map[NR_CPUS] = { [0 .. NR_CPUS-1] = CPU_MASK_NONE };
 
 EXPORT_SYMBOL(cpu_online_map);
 EXPORT_SYMBOL(cpu_possible_map);
@@ -870,6 +871,12 @@ void __init smp_prepare_cpus(unsigned in
 	for_each_cpu(cpu)
 		if (cpu != boot_cpuid)
 			smp_create_idle(cpu);
+
+	for_each_cpu(cpu) {
+		cpu_set(cpu, cpu_sibling_map[cpu]);
+		if (cur_cpu_spec->cpu_features & CPU_FTR_SMT)
+			cpu_set(cpu ^ 0x1, cpu_sibling_map[cpu]);
+	}
 }
 
 void __devinit smp_prepare_boot_cpu(void)
diff -Nurp --exclude-from=/home/mcd/.dontdiff linux-2.6.8-rc2-mm1/include/asm-ppc64/smp.h linux-2.6.8-rc2-mm1+ppc64-cpu_sibling_map/include/asm-ppc64/smp.h
--- linux-2.6.8-rc2-mm1/include/asm-ppc64/smp.h	2004-07-28 10:50:50.000000000 -0700
+++ linux-2.6.8-rc2-mm1+ppc64-cpu_sibling_map/include/asm-ppc64/smp.h	2004-07-28 12:02:38.000000000 -0700
@@ -49,6 +49,7 @@ extern cpumask_t cpu_present_at_boot;
 extern cpumask_t cpu_online_map;
 extern cpumask_t cpu_possible_map;
 extern cpumask_t cpu_available_map;
+extern cpumask_t cpu_sibling_map[NR_CPUS];
 
 #define cpu_present_at_boot(cpu) cpu_isset(cpu, cpu_present_at_boot)
 #define cpu_available(cpu)       cpu_isset(cpu, cpu_available_map) 


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