parisc: Add native high-resolution sched_clock() implementation

Add a native implementation for the sched_clock() function which utilizes the
processor-internal cycle counter (Control Register 16) as high-resolution time
source.

With this patch we now get much more fine-grained resolutions in various
in-kernel time measurements (e.g. when viewing the function tracing logs), and
probably a more accurate scheduling on SMP systems.

There are a few specific implementation details in this patch:

1. On a 32bit kernel we emulate the higher 32bits of the required 64-bit
resolution of sched_clock() by increasing a per-cpu counter at every
wrap-around of the 32bit cycle counter.

2. In a SMP system, the cycle counters of the various CPUs are not syncronized
(similiar to the TSC in a x86_64 system). To cope with this we define
HAVE_UNSTABLE_SCHED_CLOCK and let the upper layers do the adjustment work.

3. Since we need HAVE_UNSTABLE_SCHED_CLOCK, we need to provide a cmpxchg64()
function even on a 32-bit kernel.

4. A 64-bit SMP kernel which is started on a UP system will mark the
sched_clock() implementation as "stable", which means that we don't expect any
jumps in the returned counter. This is true because we then run only on one
CPU.

Signed-off-by: Helge Deller <deller@gmx.de>

1 files changed, 5 insertions, 4 deletions

diff --git a/arch/parisc/include/asm/cmpxchg.h b/arch/parisc/include/asm/cmpxchg.h
index 0a90b965cccb..7ada30900807 100644
--- a/arch/parisc/include/asm/cmpxchg.h
+++ b/arch/parisc/include/asm/cmpxchg.h
@@ -52,8 +52,7 @@ extern void __cmpxchg_called_with_bad_pointer(void);
 /* __cmpxchg_u32/u64 defined in arch/parisc/lib/bitops.c */
 extern unsigned long __cmpxchg_u32(volatile unsigned int *m, unsigned int old,
 				   unsigned int new_);
-extern unsigned long __cmpxchg_u64(volatile unsigned long *ptr,
-				   unsigned long old, unsigned long new_);
+extern u64 __cmpxchg_u64(volatile u64 *ptr, u64 old, u64 new_);
 
 /* don't worry...optimizer will get rid of most of this */
 static inline unsigned long
@@ -61,7 +60,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size)
 {
 	switch (size) {
 #ifdef CONFIG_64BIT
-	case 8: return __cmpxchg_u64((unsigned long *)ptr, old, new_);
+	case 8: return __cmpxchg_u64((u64 *)ptr, old, new_);
 #endif
 	case 4: return __cmpxchg_u32((unsigned int *)ptr,
 				     (unsigned int)old, (unsigned int)new_);
@@ -86,7 +85,7 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
 {
 	switch (size) {
 #ifdef CONFIG_64BIT
-	case 8:	return __cmpxchg_u64((unsigned long *)ptr, old, new_);
+	case 8:	return __cmpxchg_u64((u64 *)ptr, old, new_);
 #endif
 	case 4:	return __cmpxchg_u32(ptr, old, new_);
 	default:
@@ -111,4 +110,6 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
 #define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
 #endif
 
+#define cmpxchg64(ptr, o, n) __cmpxchg_u64(ptr, o, n)
+
 #endif /* _ASM_PARISC_CMPXCHG_H_ */