[PATCH] s390: spin lock retry

Split spin lock and r/w lock implementation into a single try which is done
inline and an out of line function that repeatedly tries to get the lock
before doing the cpu_relax().  Add a system control to set the number of
retries before a cpu is yielded.

The reason for the spin lock retry is that the diagnose 0x44 that is used to
give up the virtual cpu is quite expensive.  For spin locks that are held only
for a short period of time the costs of the diagnoses outweights the savings
for spin locks that are held for a longer timer.  The default retry count is
1000.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 83 insertions, 178 deletions

diff --git a/include/asm-s390/lowcore.h b/include/asm-s390/lowcore.h
index 76b5b19c0ae2..afe6a9f9b0ae 100644
--- a/include/asm-s390/lowcore.h
+++ b/include/asm-s390/lowcore.h
@@ -90,7 +90,6 @@
 #define __LC_SYSTEM_TIMER               0x278
 #define __LC_LAST_UPDATE_CLOCK          0x280
 #define __LC_STEAL_CLOCK                0x288
-#define __LC_DIAG44_OPCODE              0x290
 #define __LC_KERNEL_STACK               0xD40
 #define __LC_THREAD_INFO                0xD48
 #define __LC_ASYNC_STACK                0xD50
@@ -286,8 +285,7 @@ struct _lowcore
         __u64        system_timer;             /* 0x278 */
         __u64        last_update_clock;        /* 0x280 */
         __u64        steal_clock;              /* 0x288 */
-        __u32        diag44_opcode;            /* 0x290 */
-        __u8         pad8[0xc00-0x294];        /* 0x294 */
+        __u8         pad8[0xc00-0x290];        /* 0x290 */
         /* System info area */
         __u64        save_area[16];            /* 0xc00 */
         __u8         pad9[0xd40-0xc80];        /* 0xc80 */
diff --git a/include/asm-s390/processor.h b/include/asm-s390/processor.h
index 8bd14de69e35..4ec652ebb3b1 100644
--- a/include/asm-s390/processor.h
+++ b/include/asm-s390/processor.h
@@ -203,7 +203,10 @@ unsigned long get_wchan(struct task_struct *p);
 # define cpu_relax()    asm volatile ("diag 0,0,68" : : : "memory")
 #else /* __s390x__ */
 # define cpu_relax() \
-        asm volatile ("ex 0,%0" : : "i" (__LC_DIAG44_OPCODE) : "memory")
+        do { \
+                if (MACHINE_HAS_DIAG44) \
+                        asm volatile ("diag 0,0,68" : : : "memory"); \
+        } while (0)
 #endif /* __s390x__ */
 
 /*
diff --git a/include/asm-s390/spinlock.h b/include/asm-s390/spinlock.h
index 53cc736b9820..8ff10300f7ee 100644
--- a/include/asm-s390/spinlock.h
+++ b/include/asm-s390/spinlock.h
@@ -11,21 +11,16 @@
 #ifndef __ASM_SPINLOCK_H
 #define __ASM_SPINLOCK_H
 
-#ifdef __s390x__
-/*
- * Grmph, take care of %&#! user space programs that include
- * asm/spinlock.h. The diagnose is only available in kernel
- * context.
- */
-#ifdef __KERNEL__
-#include <asm/lowcore.h>
-#define __DIAG44_INSN "ex"
-#define __DIAG44_OPERAND __LC_DIAG44_OPCODE
-#else
-#define __DIAG44_INSN "#"
-#define __DIAG44_OPERAND 0
-#endif
-#endif /* __s390x__ */
+static inline int
+_raw_compare_and_swap(volatile unsigned int *lock,
+                      unsigned int old, unsigned int new)
+{
+        asm volatile ("cs %0,%3,0(%4)"
+                      : "=d" (old), "=m" (*lock)
+                      : "0" (old), "d" (new), "a" (lock), "m" (*lock)
+                      : "cc", "memory" );
+        return old;
+}
 
 /*
  * Simple spin lock operations.  There are two variants, one clears IRQ's
@@ -41,58 +36,35 @@ typedef struct {
 #endif
 } __attribute__ ((aligned (4))) spinlock_t;
 
-#define SPIN_LOCK_UNLOCKED (spinlock_t) { 0 }
-#define spin_lock_init(lp) do { (lp)->lock = 0; } while(0)
+#define SPIN_LOCK_UNLOCKED      (spinlock_t) { 0 }
+#define spin_lock_init(lp)      do { (lp)->lock = 0; } while(0)
 #define spin_unlock_wait(lp)    do { barrier(); } while(((volatile spinlock_t *)(lp))->lock)
-#define spin_is_locked(x) ((x)->lock != 0)
+#define spin_is_locked(x)       ((x)->lock != 0)
 #define _raw_spin_lock_flags(lock, flags) _raw_spin_lock(lock)
 
-extern inline void _raw_spin_lock(spinlock_t *lp)
+extern void _raw_spin_lock_wait(spinlock_t *lp, unsigned int pc);
+extern int _raw_spin_trylock_retry(spinlock_t *lp, unsigned int pc);
+
+static inline void _raw_spin_lock(spinlock_t *lp)
 {
-#ifndef __s390x__
-        unsigned int reg1, reg2;
-        __asm__ __volatile__("    bras  %0,1f\n"
-                           "0:  diag  0,0,68\n"
-                           "1:  slr   %1,%1\n"
-                           "    cs    %1,%0,0(%3)\n"
-                           "    jl    0b\n"
-                           : "=&d" (reg1), "=&d" (reg2), "=m" (lp->lock)
-                           : "a" (&lp->lock), "m" (lp->lock)
-                           : "cc", "memory" );
-#else /* __s390x__ */
-        unsigned long reg1, reg2;
-        __asm__ __volatile__("    bras  %1,1f\n"
-                           "0:  " __DIAG44_INSN " 0,%4\n"
-                           "1:  slr   %0,%0\n"
-                           "    cs    %0,%1,0(%3)\n"
-                           "    jl    0b\n"
-                           : "=&d" (reg1), "=&d" (reg2), "=m" (lp->lock)
-                           : "a" (&lp->lock), "i" (__DIAG44_OPERAND),
-                             "m" (lp->lock) : "cc", "memory" );
-#endif /* __s390x__ */
+        unsigned long pc = (unsigned long) __builtin_return_address(0);
+
+        if (unlikely(_raw_compare_and_swap(&lp->lock, 0, pc) != 0))
+                _raw_spin_lock_wait(lp, pc);
 }
 
-extern inline int _raw_spin_trylock(spinlock_t *lp)
+static inline int _raw_spin_trylock(spinlock_t *lp)
 {
-        unsigned long reg;
-        unsigned int result;
-
-        __asm__ __volatile__("    basr  %1,0\n"
-                           "0:  cs    %0,%1,0(%3)"
-                           : "=d" (result), "=&d" (reg), "=m" (lp->lock)
-                           : "a" (&lp->lock), "m" (lp->lock), "0" (0)
-                           : "cc", "memory" );
-        return !result;
+        unsigned long pc = (unsigned long) __builtin_return_address(0);
+
+        if (likely(_raw_compare_and_swap(&lp->lock, 0, pc) == 0))
+                return 1;
+        return _raw_spin_trylock_retry(lp, pc);
 }
 
-extern inline void _raw_spin_unlock(spinlock_t *lp)
+static inline void _raw_spin_unlock(spinlock_t *lp)
 {
-        unsigned int old;
-
-        __asm__ __volatile__("cs %0,%3,0(%4)"
-                           : "=d" (old), "=m" (lp->lock)
-                           : "0" (lp->lock), "d" (0), "a" (lp)
-                           : "cc", "memory" );
+        _raw_compare_and_swap(&lp->lock, lp->lock, 0);
 }
                 
 /*
@@ -106,7 +78,7 @@ extern inline void _raw_spin_unlock(spinlock_t *lp)
  * read-locks.
  */
 typedef struct {
-        volatile unsigned long lock;
+        volatile unsigned int lock;
         volatile unsigned long owner_pc;
 #ifdef CONFIG_PREEMPT
         unsigned int break_lock;
@@ -129,123 +101,55 @@ typedef struct {
  */
 #define write_can_lock(x) ((x)->lock == 0)
 
-#ifndef __s390x__
-#define _raw_read_lock(rw)   \
-        asm volatile("   l     2,0(%1)\n"   \
-                     "   j     1f\n"     \
-                     "0: diag  0,0,68\n" \
-                     "1: la    2,0(2)\n"     /* clear high (=write) bit */ \
-                     "   la    3,1(2)\n"     /* one more reader */ \
-                     "   cs    2,3,0(%1)\n"  /* try to write new value */ \
-                     "   jl    0b"       \
-                     : "=m" ((rw)->lock) : "a" (&(rw)->lock), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#else /* __s390x__ */
-#define _raw_read_lock(rw)   \
-        asm volatile("   lg    2,0(%1)\n"   \
-                     "   j     1f\n"     \
-                     "0: " __DIAG44_INSN " 0,%2\n" \
-                     "1: nihh  2,0x7fff\n" /* clear high (=write) bit */ \
-                     "   la    3,1(2)\n"   /* one more reader */  \
-                     "   csg   2,3,0(%1)\n" /* try to write new value */ \
-                     "   jl    0b"       \
-                     : "=m" ((rw)->lock) \
-                     : "a" (&(rw)->lock), "i" (__DIAG44_OPERAND), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#endif /* __s390x__ */
-
-#ifndef __s390x__
-#define _raw_read_unlock(rw) \
-        asm volatile("   l     2,0(%1)\n"   \
-                     "   j     1f\n"     \
-                     "0: diag  0,0,68\n" \
-                     "1: lr    3,2\n"    \
-                     "   ahi   3,-1\n"    /* one less reader */ \
-                     "   cs    2,3,0(%1)\n" \
-                     "   jl    0b"       \
-                     : "=m" ((rw)->lock) : "a" (&(rw)->lock), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#else /* __s390x__ */
-#define _raw_read_unlock(rw) \
-        asm volatile("   lg    2,0(%1)\n"   \
-                     "   j     1f\n"     \
-                     "0: " __DIAG44_INSN " 0,%2\n" \
-                     "1: lgr   3,2\n"    \
-                     "   bctgr 3,0\n"    /* one less reader */ \
-                     "   csg   2,3,0(%1)\n" \
-                     "   jl    0b"       \
-                     : "=m" ((rw)->lock) \
-                     : "a" (&(rw)->lock), "i" (__DIAG44_OPERAND), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#endif /* __s390x__ */
-
-#ifndef __s390x__
-#define _raw_write_lock(rw) \
-        asm volatile("   lhi   3,1\n"    \
-                     "   sll   3,31\n"    /* new lock value = 0x80000000 */ \
-                     "   j     1f\n"     \
-                     "0: diag  0,0,68\n" \
-                     "1: slr   2,2\n"     /* old lock value must be 0 */ \
-                     "   cs    2,3,0(%1)\n" \
-                     "   jl    0b"       \
-                     : "=m" ((rw)->lock) : "a" (&(rw)->lock), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#else /* __s390x__ */
-#define _raw_write_lock(rw) \
-        asm volatile("   llihh 3,0x8000\n" /* new lock value = 0x80...0 */ \
-                     "   j     1f\n"       \
-                     "0: " __DIAG44_INSN " 0,%2\n"   \
-                     "1: slgr  2,2\n"      /* old lock value must be 0 */ \
-                     "   csg   2,3,0(%1)\n" \
-                     "   jl    0b"         \
-                     : "=m" ((rw)->lock) \
-                     : "a" (&(rw)->lock), "i" (__DIAG44_OPERAND), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#endif /* __s390x__ */
-
-#ifndef __s390x__
-#define _raw_write_unlock(rw) \
-        asm volatile("   slr   3,3\n"     /* new lock value = 0 */ \
-                     "   j     1f\n"     \
-                     "0: diag  0,0,68\n" \
-                     "1: lhi   2,1\n"    \
-                     "   sll   2,31\n"    /* old lock value must be 0x80000000 */ \
-                     "   cs    2,3,0(%1)\n" \
-                     "   jl    0b"       \
-                     : "=m" ((rw)->lock) : "a" (&(rw)->lock), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#else /* __s390x__ */
-#define _raw_write_unlock(rw) \
-        asm volatile("   slgr  3,3\n"      /* new lock value = 0 */ \
-                     "   j     1f\n"       \
-                     "0: " __DIAG44_INSN " 0,%2\n"   \
-                     "1: llihh 2,0x8000\n" /* old lock value must be 0x8..0 */\
-                     "   csg   2,3,0(%1)\n"   \
-                     "   jl    0b"         \
-                     : "=m" ((rw)->lock) \
-                     : "a" (&(rw)->lock), "i" (__DIAG44_OPERAND), \
-                       "m" ((rw)->lock) : "2", "3", "cc", "memory" )
-#endif /* __s390x__ */
-
-#define _raw_read_trylock(lock) generic_raw_read_trylock(lock)
-
-extern inline int _raw_write_trylock(rwlock_t *rw)
+extern void _raw_read_lock_wait(rwlock_t *lp);
+extern int _raw_read_trylock_retry(rwlock_t *lp);
+extern void _raw_write_lock_wait(rwlock_t *lp);
+extern int _raw_write_trylock_retry(rwlock_t *lp);
+
+static inline void _raw_read_lock(rwlock_t *rw)
+{
+        unsigned int old;
+        old = rw->lock & 0x7fffffffU;
+        if (_raw_compare_and_swap(&rw->lock, old, old + 1) != old)
+                _raw_read_lock_wait(rw);
+}
+
+static inline void _raw_read_unlock(rwlock_t *rw)
+{
+        unsigned int old, cmp;
+
+        old = rw->lock;
+        do {
+                cmp = old;
+                old = _raw_compare_and_swap(&rw->lock, old, old - 1);
+        } while (cmp != old);
+}
+
+static inline void _raw_write_lock(rwlock_t *rw)
+{
+        if (unlikely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000) != 0))
+                _raw_write_lock_wait(rw);
+}
+
+static inline void _raw_write_unlock(rwlock_t *rw)
+{
+        _raw_compare_and_swap(&rw->lock, 0x80000000, 0);
+}
+
+static inline int _raw_read_trylock(rwlock_t *rw)
+{
+        unsigned int old;
+        old = rw->lock & 0x7fffffffU;
+        if (likely(_raw_compare_and_swap(&rw->lock, old, old + 1) == old))
+                return 1;
+        return _raw_read_trylock_retry(rw);
+}
+
+static inline int _raw_write_trylock(rwlock_t *rw)
 {
-        unsigned long result, reg;
-        
-        __asm__ __volatile__(
-#ifndef __s390x__
-                             "   lhi  %1,1\n"
-                             "   sll  %1,31\n"
-                             "   cs   %0,%1,0(%3)"
-#else /* __s390x__ */
-                             "   llihh %1,0x8000\n"
-                             "0: csg %0,%1,0(%3)\n"
-#endif /* __s390x__ */
-                             : "=d" (result), "=&d" (reg), "=m" (rw->lock)
-                             : "a" (&rw->lock), "m" (rw->lock), "0" (0UL)
-                             : "cc", "memory" );
-        return result == 0;
+        if (likely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0))
+                return 1;
+        return _raw_write_trylock_retry(rw);
 }
 
 #endif /* __ASM_SPINLOCK_H */