s390: add SMT support

The multi-threading facility is introduced with the z13 processor family.
This patch adds code to detect the multi-threading facility. With the
facility enabled each core will surface multiple hardware threads to the
system. Each hardware threads looks like a normal CPU to the operating
system with all its registers and properties.

The SCLP interface reports the SMT topology indirectly via the maximum
thread id. Each reported CPU in the result of a read-scp-information
is a core representing a number of hardware threads.

To reflect the reduced CPU capacity if two hardware threads run on a
single core the MT utilization counter set is used to normalize the
raw cputime obtained by the CPU timer deltas. This scaled cputime is
reported via the taskstats interface. The normal /proc/stat numbers
are based on the raw cputime and are not affected by the normalization.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/s390/include/asm/smp.h b/arch/s390/include/asm/smp.h
index 762d4f88af5a..b3bd0282dd98 100644
--- a/arch/s390/include/asm/smp.h
+++ b/arch/s390/include/asm/smp.h
@@ -16,6 +16,8 @@
 #define raw_smp_processor_id()	(S390_lowcore.cpu_nr)
 
 extern struct mutex smp_cpu_state_mutex;
+extern unsigned int smp_cpu_mt_shift;
+extern unsigned int smp_cpu_mtid;
 
 extern int __cpu_up(unsigned int cpu, struct task_struct *tidle);
 
@@ -35,6 +37,8 @@ extern void smp_fill_possible_mask(void);
 
 #else /* CONFIG_SMP */
 
+#define smp_cpu_mtid	0
+
 static inline void smp_call_ipl_cpu(void (*func)(void *), void *data)
 {
 	func(data);