On Wed, Jan 09, 2019 at 05:19:48AM +0100, Mike Galbraith wrote: > > To test I used this trivial program. > > Which highlights the problem. That proggy really is synchronous, but > the sync hint is applied to many MANY real world cases where this is > not the case at all. Sure, you can make things like pipe_test and > nearly nonexistent payload TCP_RR numbers look gorgeous, but that > demolishes concurrency for real applications. >
I agree with Mike here. Many previous attempts to strictly obey the strict hint has led to regressions elsewhere -- specifically a task waking 2+ wakees that temporarily stack on one CPU when nearby CPUs sharing LLC remain idle. It's why the select idle sibling logic tried to take into account a recently used CPU to wake such tasks if the recent CPU was still idle. -- Mel Gorman SUSE Labs
