On Sat, 2011-01-01 at 21:51 +0100, Arjan Koers wrote: > Reduce the number of while-loop iterations (from two to one in the most > common situation) > > Signed-off-by: Arjan Koers <[email protected]> > > diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c > index 42eb330..8f52acb 100644 > --- a/arch/x86/kernel/pvclock.c > +++ b/arch/x86/kernel/pvclock.c > @@ -93,7 +93,7 @@ cycle_t pvclock_clocksource_read(struct > pvclock_vcpu_time_info *src) > struct pvclock_shadow_time shadow; > unsigned version; > cycle_t ret, offset; > - u64 last; > + u64 last, save; > > do { > version = pvclock_get_time_values(&shadow, src); > @@ -125,8 +125,9 @@ cycle_t pvclock_clocksource_read(struct > pvclock_vcpu_time_info *src) > do { > if (ret < last) > return last; > + save = last; > last = atomic64_cmpxchg(&last_value, last, ret); > - } while (unlikely(last != ret)); > + } while (unlikely(last != save)); > > return ret; > } Hey, good catch.
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