On Wed, Oct 21, 2020 at 03:24:48PM +0200, Julia Lawall wrote: > > I worry it's overkill because prev is always used if it is idle even > > if it is on a node remote to the waker. It cuts off the option of a > > wakee moving to a CPU local to the waker which is not equivalent to the > > original behaviour. > > But it is equal to the original behavior in the idle prev case if you go > back to the runnable load average days... > It is similar but it misses the sync treatment and sd->imbalance_pct part of wake_affine_weight which has unpredictable consequences. The data available is only on the fully utilised case. > The problem seems impossible to solve, because there is no way to know by > looking only at prev and this whether the thread would prefer to stay > where it was or go to the waker. > Yes, this is definitely true. Looking at prev_cpu and this_cpu is a crude approximation and the path is heavily limited in terms of how clever it can be. -- Mel Gorman SUSE Labs
