s390/spinlock: add compare-and-delay to lock wait loops

Add the compare-and-delay instruction to the spin-lock and rw-lock
retry loops. A CPU executing the compare-and-delay instruction stops
until the lock value has changed. This is done to make the locking
code for contended locks to behave better in regard to the multi-
hreading facility. A thread of a core executing a compare-and-delay
will allow the other threads of a core to get a larger share of the
core resources.

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

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 302ac1f7f8e7..70a329450901 100644
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -393,9 +393,27 @@ 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)
+{
+        S390_lowcore.machine_flags &= ~MACHINE_FLAG_CAD;
+        return 0;
+}
+early_param("nocad", nocad_setup);
+
+static int __init cad_init(void)
+{
+        if (MACHINE_HAS_CAD)
+                /* Enable problem state CAD. */
+                __ctl_set_bit(2, 3);
+        return 0;
+}
+early_initcall(cad_init);
+
 static __init void rescue_initrd(void)
 {
 #ifdef CONFIG_BLK_DEV_INITRD