[Openmp-commits] [PATCH] D132005: [OpenMP] Add non-blocking support for target nowait regions

[Guilherme Valarini via Phabricator via Openmp-commits]

gValarini added a comment.

In D132005#3883907 <https://reviews.llvm.org/D132005#3883907>, @tianshilei1992 wrote:

> TBH I'd like to see/understand if task yield is worse than this method. If not, I'm not sure why we'd like to have so many complicated code.

Sorry, I missed your previous comment before.

I believe this method can be better than using task yield because it has less probability of "starvation", let me explain. AFAIK, task yield is currently being implemented by calling other tasks in the middle of the execution of the current task, meaning the task execution state (and ordering of resumption) is stored inside the call stack. This can incur a "starvation-like" problem, where an earlier task that has its operations completed cannot be finished because it is at the bottom of the call stack. This can also hold other tasks that are dependent on this "starved" one. Another problem is that, depending on the number of ready target regions, a program can even surpass the stack limit due to many in-flight tasks. If task yield were implemented in a coroutine-like model (maybe some future work), where yielded tasks could be re-enqueued and re-ordered, we would probably use it since that makes the code much simpler.

Another thing is that this can also be an initial point of integration for the device-side resolution of dependencies. (although D81989 <https://reviews.llvm.org/D81989> also did that as well).


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