s390/spinlock: disabled compare-and-delay by default

Until we have hard performance data about the effects of CAD in the
spinlock loop disable the instruction by default.

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

1 files changed, 7 insertions, 5 deletions

diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 70a329450901..4427ab7ac23a 100644
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -393,17 +393,19 @@ static __init void detect_machine_facilities(void)
                 S390_lowcore.machine_flags |= MACHINE_FLAG_TLB_LC;
         if (test_facility(129))
                 S390_lowcore.machine_flags |= MACHINE_FLAG_VX;
-        if (test_facility(128))
-                S390_lowcore.machine_flags |= MACHINE_FLAG_CAD;
 #endif
 }
 
-static int __init nocad_setup(char *str)
+static int __init cad_setup(char *str)
 {
-        S390_lowcore.machine_flags &= ~MACHINE_FLAG_CAD;
+        int val;
+
+        get_option(&str, &val);
+        if (val && test_facility(128))
+                S390_lowcore.machine_flags |= MACHINE_FLAG_CAD;
         return 0;
 }
-early_param("nocad", nocad_setup);
+early_param("cad", cad_setup);
 
 static int __init cad_init(void)
 {