tree 7ed16d9d49aa382e151af7dd5fe57bf2120a6423
parent acb2548ddecbc26d46c28b1cd799fe4ca18f8914
author Jonathan Peyton <jonathan.l.peyton@intel.com> 1551381089 +0000
committer Jonathan Peyton <jonathan.l.peyton@intel.com> 1551381089 +0000

[OpenMP] Make use of sched_yield optional in runtime

This patch cleans up the yielding code and makes it optional. An
environment variable, KMP_USE_YIELD, was added. Yielding is still
on by default (KMP_USE_YIELD=1), but can be turned off completely
(KMP_USE_YIELD=0), or turned on only when oversubscription is detected
(KMP_USE_YIELD=2). Note that oversubscription cannot always be detected
by the runtime (for example, when the runtime is initialized and the
process forks, oversubscription cannot be detected currently over
multiple instances of the runtime).

Because yielding can be controlled by user now, the library mode
settings (from KMP_LIBRARY) for throughput and turnaround have been
adjusted by altering blocktime, unless that was also explicitly set.

In the original code, there were a number of places where a double yield
might have been done under oversubscription. This version checks
oversubscription and if that's not going to yield, then it does
the spin check.

Patch by Terry Wilmarth

Differential Revision: https://reviews.llvm.org/D58148


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@355120 91177308-0d34-0410-b5e6-96231b3b80d8