[S390] cpu topology: introduce kernel parameter

Introduce a topology=[on|off] kernel parameter which allows to switch
cpu topology on/off. Default will be off, since it looks like that for
some workloards this doesn't behave very well (on s390).

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

2 files changed, 19 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c9115c1b672c..09ede6c90ad7 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2252,6 +2252,14 @@ and is between 256 and 4096 characters. It is defined in the file
                         See comment before function dc390_setup() in
                         drivers/scsi/tmscsim.c.
 
+        topology=       [S390]
+                        Format: {off | on}
+                        Specify if the kernel should make use of the cpu
+                        topology informations if the hardware supports these.
+                        The scheduler will make use of these informations and
+                        e.g. base its process migration decisions on it.
+                        Default is off.
+
         tp720=          [HW,PS2]
 
         trix=           [HW,OSS] MediaTrix AudioTrix Pro
diff --git a/arch/s390/kernel/topology.c b/arch/s390/kernel/topology.c
index 36faac50e774..71e6f56bfead 100644
--- a/arch/s390/kernel/topology.c
+++ b/arch/s390/kernel/topology.c
@@ -58,6 +58,7 @@ struct core_info {
         cpumask_t mask;
 };
 
+static int topology_enabled;
 static void topology_work_fn(struct work_struct *work);
 static struct tl_info *tl_info;
 static struct core_info core_info;
@@ -78,7 +79,7 @@ cpumask_t cpu_coregroup_map(unsigned int cpu)
         cpumask_t mask;
 
         cpus_clear(mask);
-        if (!machine_has_topology)
+        if (!topology_enabled || !machine_has_topology)
                 return cpu_possible_map;
         spin_lock_irqsave(&topology_lock, flags);
         while (core) {
@@ -263,6 +264,15 @@ static void topology_interrupt(__u16 code)
         schedule_work(&topology_work);
 }
 
+static int __init early_parse_topology(char *p)
+{
+        if (strncmp(p, "on", 2))
+                return 0;
+        topology_enabled = 1;
+        return 0;
+}
+early_param("topology", early_parse_topology);
+
 static int __init init_topology_update(void)
 {
         int rc;