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 <0h61vkll2ly8@xxxxxxxxxx>
>
> 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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