[S390] Vertical cpu management.

If vertical cpu polarization is active then the hypervisor will
dispatch certain cpus for a longer time than other cpus for maximum
performance. For example if a guest would have three virtual cpus,
each of them with a share of 33 percent, then in case of vertical
cpu polarization all of the processing time would be combined to a
single cpu which would run all the time, while the other two cpus
would get nearly no cpu time.

There are three different types of vertical cpus: high, medium and
low. Low cpus hardly get any real cpu time, while high cpus get a
full real cpu. Medium cpus get something in between.

In order to switch between the two possible modes (default is
horizontal) a 0 for horizontal polarization or a 1 for vertical
polarization must be written to the dispatching sysfs attribute:

/sys/devices/system/cpu/dispatching

The polarization of each single cpu can be figured out by the
polarization sysfs attribute of each cpu:

/sys/devices/system/cpu/cpuX/polarization

horizontal, vertical:high, vertical:medium, vertical:low or unknown.

When switching polarization the polarization attribute may contain
the value unknown until the configuration change is done and the
kernel has figured out the new polarization of each cpu.

Note that running a system with different types of vertical cpus may
result in significant performance regressions. If possible only one
type of vertical cpus should be used. All other cpus should be
offlined.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

2 files changed, 10 insertions, 0 deletions

diff --git a/include/asm-s390/smp.h b/include/asm-s390/smp.h
index a464a66c65d3..6f3821a6a902 100644
--- a/include/asm-s390/smp.h
+++ b/include/asm-s390/smp.h
@@ -91,6 +91,7 @@ extern void cpu_die (void) __attribute__ ((noreturn));
 extern int __cpu_up (unsigned int cpu);
 
 extern struct mutex smp_cpu_state_mutex;
+extern int smp_cpu_polarization[];
 
 extern int smp_call_function_mask(cpumask_t mask, void (*func)(void *),
         void *info, int wait);
diff --git a/include/asm-s390/topology.h b/include/asm-s390/topology.h
index 3b28a09a2108..8e97b06f298a 100644
--- a/include/asm-s390/topology.h
+++ b/include/asm-s390/topology.h
@@ -7,6 +7,15 @@
 
 cpumask_t cpu_coregroup_map(unsigned int cpu);
 
+int topology_set_cpu_management(int fc);
+void topology_schedule_update(void);
+
+#define POLARIZATION_UNKNWN     (-1)
+#define POLARIZATION_HRZ        (0)
+#define POLARIZATION_VL         (1)
+#define POLARIZATION_VM         (2)
+#define POLARIZATION_VH         (3)
+
 #ifdef CONFIG_SMP
 void s390_init_cpu_topology(void);
 #else