https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604
--- Comment #24 from Alexander Nesterovskiy <alexander.nesterovskiy at intel dot com> --- Yes, it looks like more time is being spent in synchronizing. r256990 really changes the way autopar works: For r253679...r256989 the most of work was in main thread0 mostly (thread0 ~91%, threads1-3 ~3% each one). For r256990 there is the same distribution as for r253678 (thread0 ~34%, threads1-3 ~22% each one) but a lot of time is being spent spinning. I've attached a chart comparing r253678 and r256990 in the same time scale (~0.5 sec). libgomp.so.1.0.0 code executed in thread1 for both cases is wait functions, and for r256990 they are called more often. Setting OMP_WAIT_POLICY doesn't change a lot: for ACTIVE - performance is nearly the same as default for PASSIVE - there is a serious performance drop for r256990 (looks reasonable because of a lots of threads sleeps/wake-ups) Changing parloops-schedule also have no positive effect: r253678 performance is mostly the same for static, guided and dynamic r256990 performance is best with static, which is default
