[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>

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 */