[patch 49/67] SPARC64: Fix serious bug in sched_clock() on sparc64

Greg KH
2006-10-11T21:19:05Z

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-stable review patch. If anyone has any objections, please let us know.

------------------
From: David S. Miller <davem@davemloft.net>

Unfortunately, sparc64 doesn't have an easy way to do a "64 X 64 -->
128" bit multiply like PowerPC and IA64 do. We were doing a
"64 X 64 --> 64" bit multiple which causes overflow very quickly with
a 30-bit quotient shift.

So use a quotientshift count of 10 instead of 30, just like x86 and
ARM do.

This also fixes the wrapping of printk timestamp values every ~17
seconds.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/sparc64/kernel/time.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-2.6.18.orig/arch/sparc64/kernel/time.c
+++ linux-2.6.18/arch/sparc64/kernel/time.c
@@ -983,7 +983,7 @@ static struct time_interpolator sparc64_
};

/* The quotient formula is taken from the IA64 port. */
-#define SPARC64_NSEC_PER_CYC_SHIFT 30UL
+#define SPARC64_NSEC_PER_CYC_SHIFT 10UL
void __init time_init(void)
{
unsigned long clock = sparc64_init_timers();

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