Re: [PATCH v3] cpuidle: Fix last_residency division

On 06/29/2016 08:31 PM, Nicolas Pitre wrote:

On Wed, 29 Jun 2016, Daniel Lezcano wrote:

quoted

On 06/29/2016 09:06 AM, Shreyas B. Prabhu wrote:

quoted

diff --git a/drivers/cpuidle/cpuidle.h b/drivers/cpuidle/cpuidle.h
index f87f399..c8ea5ad 100644
--- a/drivers/cpuidle/cpuidle.h
+++ b/drivers/cpuidle/cpuidle.h

@@ -68,4 +68,27 @@ static inline void

cpuidle_coupled_unregister_device(struct cpuidle_device *dev)
  }
  #endif

+/*
+ * Used for calculating last_residency in usec. Optimized for case
+ * where last_residency in nsecs is < INT_MAX/2 by using faster
+ * approximation. Approximated value has less than 1% error.
+ */
+static inline int convert_nsec_to_usec(u64 nsec)
+{
+	if (likely(nsec < INT_MAX / 2)) {

UINT_MAX ?

Actually this can be better than that.

quoted

quoted

+		int usec = (int)nsec;

First, you'll want an unsigned type. Given the provided argument is u64, 
we can assume there won't be any negative values here.

Then it would be wise to use a type with an explicit width, like U32.

Cool. I wanted to avoid multiple casts. i.e u64 -> u32 -> int. But I
guess there is no real need to avoid it.

Sending v4 with your suggestions.

Thanks,
Shreyas