On Wed, 15 Feb, at 04:12:11PM, Frederic Weisbecker wrote: > On Wed, Feb 08, 2017 at 01:29:24PM +0000, Matt Fleming wrote: > > The calculation for the next sample window when exiting NOH_HZ idle > > does not handle the fact that we may not have reached the next sample > > window yet > > That sentence is hard to parse, it took me some time to figure out that > those two "next sample window" may not refer to the same thing. Yeah, it's not the most lucid thing I've ever written. > Maybe it would be clearer with something along the lines of: > > "The calculation for the next sample window when exiting NO_HZ > does not handle the fact that we may not have crossed any sample > window during the NO_HZ period." Umm... this isn't the problem. In fact, it's the opposite. The problem is that if we *did* cross a sample window while in NO_HZ, then when we exit the pending window may be far enough into the future that all we need to do is update this_rq->calc_load_update. > > If we wake from NO_HZ idle after the pending this_rq->calc_load_update > > window time when we want idle but before the next sample window > > That too was hard to understand. How about: > > "If we enter in NO_HZ mode after a pending this_rq->calc_load_update > and we exit from NO_HZ mode before the forthcoming sample window, ..." You've got this backwards again. We enter NO_HZ before the pending window, not after.