Switch to task-focused synchronization model #374
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jpsamaroo
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That's awesome @jpsamaroo ! Thanks, we will look into this with @omlins and @utkinis to finalise AMDGPU support in ImplicitGlobalGrid.jl and ParallelStencil.jl. |
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Add HIPDevice and HIPStream abstractions Add `synchronize(::HIPStream)`
Stores a task-local device, queue, context, and stream via `task_local_storage`. Task state can be accessed with `task_local_state`, and stored with `task_local_state!`. The `task_local_state!` function has a functional form for locally-scoped task state changes. `device()`, `queue()`, `context()`, and `stream()` are available to query TLS for their appropriate values, and `device!()`, `queue!()`, and `stream!()` can be used to set a new value in TLS. Additionally, queue and stream priorities are accessible with `priority()` and settable with `priority!()`. `default_queue()` now forwards to `queue()`, and is deprecated. `default_device()` and friends still work globally, but users should prefer to use `device()` and `device!()` instead. There is no longer a single default queue per device; instead, queues are pooled per-device and are assigned to tasks in a round-robin fashion. Separate pool sizes are configurable on a per-queue-priority basis. Active kernel tracking is now handled by a per-queue background task which waits on and cleans up the active kernel list (which is now moved into the `ROCQueue` object). A new function `synchronize()` is available to wait on all currently-active kernels on the current queue and/or stream to complete.
Switch library handles to be allocated per-task Copy HandleCache mechanism from CUDA.jl Always include library wrapper code
Also use `queue` instead of `default_queue` to avoid triggering depwarn.
- Use current default device when creating HIPStream from raw hipStream_t. Since there appears to be no way to get the device from just hipStream_t. - Use passed device in TLS for HIPStream creation.
- Construct HIPStream using device from current HIPContext. - Add docs clarifying distinction between `get_default_device()` & `device()`.
This linked list is append-only and singly-linked, and allows multiple threads to concurrently read from it, while one task may advance the list head serially.
Uses the new `LinkedList` in place of `Vector` for active kernel tracking, which allows mostly-lockless concurrent access to the active kernel set, often with no or minimal allocations. Propagates errors from the current or prior kernels in `synchronize` by default, and adds an `errors::Bool` kwarg to `synchronize` to allow skipping error checking if desired. Disables all kernel resource cleanup during `wait`, and instead moves this fully into the kernel monitor. Also fixes a bug in the kernel monitor where a dead queue may not have all kernel resources cleaned up. Removes auto-reset of the queue in TLS, and instead provides `reset_dead_queue!()` to reset the queue if it's dead. Properly catches and ignores kernel errors in the queue monitor. Makes the `queue` field in `ROCQueue` no longer atomic, as we do not change it.
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This PR switches AMDGPU to a task-focused synchronization model, similar to CUDA.jl. In such a model, tasks have their own device and queue assigned, and all GPU operations on that task are launched in serial. That is to say, kernels don't start until any previously-launched kernels have completed. It is thus no longer necessary to
waiton the result of@roc, and instead, one can callAMDGPU.synchronize()on the host to wait for all currently-executing kernels (launched from this task) to complete.There are many reasons why we'd want to switch to this model:
The existing
wait-focused model is still fully available, so for the most part, behavior remains the same (assuming users were previously only using one task to launch GPU kernels); the previous single-queue behavior can be enabled by callingAMDGPU.Runtime.set_alloc_queue_pool_max!([1,0,0]), which shares a single queue per device, and disables the queue pooling logic for low- and high-priority queues.Todo:
ROCKernelSignalsynchronize()by default, make sure that errors do print in background