[Openmp-commits] [PATCH] D63009: [OpenMP] Add target task alloc function with device ID

Alexandre Eichenberger via Phabricator via Openmp-commits openmp-commits at lists.llvm.org
Fri Jun 14 12:02:34 PDT 2019

AlexEichenberger added inline comments.

Comment at: lib/CodeGen/CGOpenMPRuntime.cpp:5122
+    NewTask = CGF.EmitRuntimeCall(
+      createRuntimeFunction(OMPRTL__kmpc_omp_target_task_alloc), AllocArgs);
+  } else {
gtbercea wrote:
> ABataev wrote:
> > gtbercea wrote:
> > > ABataev wrote:
> > > > gtbercea wrote:
> > > > > ABataev wrote:
> > > > > > gtbercea wrote:
> > > > > > > ABataev wrote:
> > > > > > > > Can we use the same function in both modes, with nowait clause and without?
> > > > > > > For nowait we need to use the target_task_alloc variant. There are runtimes - other than the open source one - for which this function does something different.
> > > > > > Trunk relies only to libomptarget interfaces. Why we should take into account some other runtime libraries? Plus, what's so different for async and non-async versions of the directive?
> > > > > Async is not yet fully supported in the OpenMP open source runtime but at some point it will be. This is the first step towards its support. I'm not sure what your objection is. The difference is clear. Device ID must be passed on the async version of this call.
> > > > The difference is not obvious. Why we can't use the same function for sync directives? The fact the it has DeviceId parameter is not an argument here. What's so special from functional point of view?
> > > When you have multiple device on the same system you have to be able to distinguish between then and manage dependencies across these different devices. Knowing the device is a crucial first step in handling these inter-device dependencies.
> > Ok, this is why we need it for async version. But why we can't use for sync version?
> Based on how the runtime is currently structured, nowait functions are separate from the synchronous ones. See target vs. target_nowait functions and there are many examples like that. The async support is always kept separate from the synchronous support at least in terms of entry points in the runtime.
Right now, target_task indicates two things: 1) there are depenences to offload and 2) it's a nowait constructs. If we use target_task_alloc for both situations, we need to distinguish these two cases using flags, because the handling iseventually different.
If we want to explore this avenue, then we have to look into using the proxy flag is set to indicates nowait. It may have implications for the tasks on the KMP side, so this might be more risky.
This is why I suggest at the present time that we only generate target task for the limited "target task depend nowait"

  rC Clang



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