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, 45 insertions, 7 deletions

diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index 034a35a3e9c1..d6c9991f7797 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -12,7 +12,15 @@
 #include <linux/smp.h>
 #include <asm/io.h>
 
-int spin_retry = 1000;
+int spin_retry = -1;
+
+static int __init spin_retry_init(void)
+{
+        if (spin_retry < 0)
+                spin_retry = MACHINE_HAS_CAD ? 10 : 1000;
+        return 0;
+}
+early_initcall(spin_retry_init);
 
 /**
  * spin_retry= parameter
@@ -24,6 +32,11 @@ static int __init spin_retry_setup(char *str)
 }
 __setup("spin_retry=", spin_retry_setup);
 
+static inline void _raw_compare_and_delay(unsigned int *lock, unsigned int old)
+{
+        asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old), "Q" (*lock));
+}
+
 void arch_spin_lock_wait(arch_spinlock_t *lp)
 {
         unsigned int cpu = SPINLOCK_LOCKVAL;
@@ -46,6 +59,8 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
                 /* Loop for a while on the lock value. */
                 count = spin_retry;
                 do {
+                        if (MACHINE_HAS_CAD)
+                                _raw_compare_and_delay(&lp->lock, owner);
                         owner = ACCESS_ONCE(lp->lock);
                 } while (owner && count-- > 0);
                 if (!owner)
@@ -84,6 +99,8 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
                 /* Loop for a while on the lock value. */
                 count = spin_retry;
                 do {
+                        if (MACHINE_HAS_CAD)
+                                _raw_compare_and_delay(&lp->lock, owner);
                         owner = ACCESS_ONCE(lp->lock);
                 } while (owner && count-- > 0);
                 if (!owner)
@@ -100,11 +117,19 @@ EXPORT_SYMBOL(arch_spin_lock_wait_flags);
 
 int arch_spin_trylock_retry(arch_spinlock_t *lp)
 {
+        unsigned int cpu = SPINLOCK_LOCKVAL;
+        unsigned int owner;
         int count;
 
-        for (count = spin_retry; count > 0; count--)
-                if (arch_spin_trylock_once(lp))
-                        return 1;
+        for (count = spin_retry; count > 0; count--) {
+                owner = ACCESS_ONCE(lp->lock);
+                /* Try to get the lock if it is free. */
+                if (!owner) {
+                        if (_raw_compare_and_swap(&lp->lock, 0, cpu))
+                                return 1;
+                } else if (MACHINE_HAS_CAD)
+                        _raw_compare_and_delay(&lp->lock, owner);
+        }
         return 0;
 }
 EXPORT_SYMBOL(arch_spin_trylock_retry);
@@ -126,8 +151,11 @@ void _raw_read_lock_wait(arch_rwlock_t *rw)
                 }
                 old = ACCESS_ONCE(rw->lock);
                 owner = ACCESS_ONCE(rw->owner);
-                if ((int) old < 0)
+                if ((int) old < 0) {
+                        if (MACHINE_HAS_CAD)
+                                _raw_compare_and_delay(&rw->lock, old);
                         continue;
+                }
                 if (_raw_compare_and_swap(&rw->lock, old, old + 1))
                         return;
         }
@@ -141,8 +169,11 @@ int _raw_read_trylock_retry(arch_rwlock_t *rw)
 
         while (count-- > 0) {
                 old = ACCESS_ONCE(rw->lock);
-                if ((int) old < 0)
+                if ((int) old < 0) {
+                        if (MACHINE_HAS_CAD)
+                                _raw_compare_and_delay(&rw->lock, old);
                         continue;
+                }
                 if (_raw_compare_and_swap(&rw->lock, old, old + 1))
                         return 1;
         }
@@ -173,6 +204,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int prev)
                 }
                 if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
                         break;
+                if (MACHINE_HAS_CAD)
+                        _raw_compare_and_delay(&rw->lock, old);
         }
 }
 EXPORT_SYMBOL(_raw_write_lock_wait);
@@ -201,6 +234,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
                         smp_rmb();
                 if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
                         break;
+                if (MACHINE_HAS_CAD)
+                        _raw_compare_and_delay(&rw->lock, old);
         }
 }
 EXPORT_SYMBOL(_raw_write_lock_wait);
@@ -214,8 +249,11 @@ int _raw_write_trylock_retry(arch_rwlock_t *rw)
 
         while (count-- > 0) {
                 old = ACCESS_ONCE(rw->lock);
-                if (old)
+                if (old) {
+                        if (MACHINE_HAS_CAD)
+                                _raw_compare_and_delay(&rw->lock, old);
                         continue;
+                }
                 if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000))
                         return 1;
         }