Current clocksource_cyc2ns() has a implicit limit that the (cycles * mult)
can not exceed 64 bits limit. Jason Gunthorpe proposed a way to
handle this big cycles case, and this patch put the handling into
clocksource_cyc2ns() so that it could be used unconditionally.
Suggested-by: Jason Gunthorpe <jguntho...@obsidianresearch.com>
Signed-off-by: Feng Tang <feng.t...@intel.com>
---
include/linux/clocksource.h | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index aa7032c..1ecc872 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -274,7 +274,16 @@ static inline u32 clocksource_hz2mult(u32 hz, u32
shift_constant)
*/
static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
{
- return ((u64) cycles * mult) >> shift;
+ u64 max = ULLONG_MAX / mult;
+ s64 nsec = 0;
+
+ /* The (mult * cycles) may overflow 64 bits, so add a max check */
+ if (cycles > max) {
+ nsec = ((max * mult) >> shift) * (cycles / max);
+ cycles %= max;
+ }
+ nsec += ((u64) cycles * mult) >> shift;
+ return nsec;
}
--
1.7.9.5
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