On Wed, Jan 20, 2016 at 02:17:57PM -0500, Nicolas Pitre wrote:

quoted

It is also a friggin pointless /1000. The cpuidle code also loves to do
this, and its silly, u64 add/sub are _way_ cheaper than u64 / 1000.

For the purpose of this code, nanoseconds simply provides too many bits 
for what we care.  Computing the variance implies squared values.

*However* we can simply do diff = (timestamp - w->timestamp) >> 10 
instead.  No need to have an exact microsecs base.

Right, you could also reduce bits at the variance computation, but yes.