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35 /*! \libinternal \file
36 * \brief Implements a GpuEventSynchronizer class for SYCL.
38 * This implementation relies on SYCL_INTEL_enqueue_barrier proposal,
39 * https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/EnqueueBarrier/enqueue_barrier.asciidoc
41 * Using event-based synchronization is not recommended for SYCL.
42 * SYCL queues are out-of-order and rely on data dependencies, allowing only to wait
43 * for a specific kernel (by capturing the \c event returned from \c queue.submit) or for all
44 * the tasks in the queue (\c queue.wait).
46 * \author Erik Lindahl <erik.lindahl@gmail.com>
47 * \author Andrey Alekseenko <al42and@gmail.com>
50 #ifndef GMX_GPU_UTILS_GPUEVENTSYNCHRONIZER_SYCL_H
51 #define GMX_GPU_UTILS_GPUEVENTSYNCHRONIZER_SYCL_H
55 #include "gromacs/gpu_utils/device_stream.h"
56 #include "gromacs/gpu_utils/gmxsycl.h"
57 #include "gromacs/utility/exceptions.h"
58 #include "gromacs/utility/gmxassert.h"
61 /*! \libinternal \brief
62 * A class which allows for CPU thread to mark and wait for certain GPU stream execution point.
63 * The event can be put into the stream with markEvent() and then later waited on with waitForEvent().
64 * This can be repeated as necessary, but the current implementation does not allow waiting on
65 * completed event more than once, expecting only exact pairs of markEvent(stream); waitForEvent().
66 * The class generally attempts to track the correctness of its state transitions, but
67 * please note that calling waitForEvent() right after the construction will fail with OpenCL
68 * and SYCL but succeed with CUDA.
70 * Another possible mode of operation can be implemented if needed:
71 * multiple calls to waitForEvent() after a single markEvent(). For this, event.reset() call
72 * from waitForEvent() should instead happen conditionally at the beginning of markEvent(), replacing
73 * the GMX_ASSERT(). This was tested to work both with CUDA, NVidia OpenCL, and Intel SYCL,
74 * but not with AMD/Intel OpenCl.
76 * \warning This class is offered for uniformity with other GPU implementations, but expect it to
77 * be deprecated in the future.
80 class GpuEventSynchronizer
84 GpuEventSynchronizer()
86 doNotSynchronizeBetweenStreams_ = (std::getenv("GMX_GPU_SYCL_NO_SYNCHRONIZE") != nullptr);
88 //! A constructor from an existing event.
89 GpuEventSynchronizer(const cl::sycl::event& event) : event_(event) {}
91 ~GpuEventSynchronizer() = default;
93 GpuEventSynchronizer(const GpuEventSynchronizer&) = delete;
95 GpuEventSynchronizer& operator=(GpuEventSynchronizer&&) = delete;
96 //! Moving is disabled but can be considered in the future if needed
97 GpuEventSynchronizer(GpuEventSynchronizer&&) = delete;
99 /*! \brief Marks the synchronization point in the \p deviceStream.
100 * Should be called first and then followed by waitForEvent() or enqueueWaitEvent().
102 inline void markEvent(const DeviceStream& deviceStream)
104 # if GMX_SYCL_HIPSYCL
105 deviceStream.stream().wait_and_throw(); // SYCL-TODO: Use CUDA/HIP-specific solutions
107 GMX_ASSERT(!event_.has_value(), "Do not call markEvent more than once!");
108 // Relies on SYCL_INTEL_enqueue_barrier
109 event_ = deviceStream.stream().submit_barrier();
112 /*! \brief Synchronizes the host thread on the marked event.
113 * As in the OpenCL implementation, the event is released.
115 inline void waitForEvent()
117 # if (!GMX_SYCL_HIPSYCL)
118 event_->wait_and_throw();
122 /*! \brief Checks the completion of the underlying event and resets the object if it was. */
123 inline bool isReady()
125 auto info = event_->get_info<cl::sycl::info::event::command_execution_status>();
126 bool hasTriggered = (info == cl::sycl::info::event_command_status::complete);
133 /*! \brief Enqueues a wait for the recorded event in stream \p deviceStream.
134 * As in the OpenCL implementation, the event is released.
136 inline void enqueueWaitEvent(const DeviceStream& deviceStream)
138 if (doNotSynchronizeBetweenStreams_)
143 # if GMX_SYCL_HIPSYCL
144 deviceStream.stream().wait_and_throw(); // SYCL-TODO: Use CUDA/HIP-specific solutions
146 // Relies on SYCL_INTEL_enqueue_barrier
147 const std::vector<cl::sycl::event> waitlist{ event_.value() };
148 deviceStream.stream().submit_barrier(waitlist);
152 //! Reset the event to unmarked state.
153 inline void reset() { event_.reset(); }
154 //! Check if the event is marked. Needed for some workarounds for #3988
155 inline bool isMarked() const { return event_.has_value(); }
158 std::optional<cl::sycl::event> event_ = std::nullopt;
159 /*! \brief Dev. setting to no-op enqueueWaitEvent
161 * In SYCL, dependencies between the GPU tasks are managed by the runtime, so manual
162 * synchronization between GPU streams should be redundant, but we keep it on by default.
164 * Setting this to \c true via \c GMX_GPU_SYCL_NO_SYNCHRONIZE environment variable will
165 * immediately return from \ref enqueueWaitEvent, without placing a barrier into the stream.
167 bool doNotSynchronizeBetweenStreams_;
170 #endif // !defined DOXYGEN
172 #endif // GMX_GPU_UTILS_GPUEVENTSYNCHRONIZER_SYCL_H