[SYCL] Add a low_power property for reusable SYCL events to reduce the CPU time spent checking wait completion conditions

[dyniols]

This PR adds the feature requested in: CMPLRLLVM-77704

[Copilot]

🟢 Approval recommended

The implementation and test coverage are coherent; only a minor documentation cross-reference remains.

Pull request overview

Adds a reusable-event low_power property, propagating it through SYCL and Unified Runtime to Level Zero v2 event synchronization.

Changes:

• Adds SYCL and UR low-power property/descriptor APIs.
• Maps the hint to Level Zero low-power event flags.
• Adds unit, conformance, and end-to-end coverage.

File summaries

File	Description
unified-runtime/test/conformance/exp_reusable_events/reusable_events.cpp	Tests low-power reusable events.
unified-runtime/source/loader/ur_print.cpp	Adds descriptor printers.
unified-runtime/source/loader/loader.map.in	Exports new printers on ELF.
unified-runtime/source/loader/loader.def.in	Exports new printers on Windows.
unified-runtime/source/common/stype_map_helpers.def	Maps the new structure type.
unified-runtime/source/adapters/level_zero/v2/event.cpp	Reads and maps the sync descriptor.
unified-runtime/source/adapters/level_zero/v2/event_provider.hpp	Adds the low-power provider flag.
unified-runtime/source/adapters/level_zero/v2/event_provider_normal.cpp	Configures low-power pooled events.
unified-runtime/source/adapters/level_zero/v2/event_provider_counter.cpp	Configures low-power counter events.
unified-runtime/source/adapters/level_zero/context.hpp	Uses the shared sync-mode definitions.
unified-runtime/source/adapters/level_zero/common/event_sync_modes.hpp	Centralizes Level Zero definitions.
unified-runtime/scripts/core/exp-reusable-events.yml	Defines the UR extension API.
unified-runtime/include/unified-runtime/ur_print.hpp	Adds generated C++ printing support.
unified-runtime/include/unified-runtime/ur_print.h	Declares generated print APIs.
unified-runtime/include/unified-runtime/ur_api.h	Adds generated UR types and flags.
sycl/unittests/Extensions/ReusableEvents.cpp	Verifies descriptor propagation.
sycl/test-e2e/Experimental/reusable_events/low_power_event_sync_mode.cpp	Exercises low-power signaling end to end.
sycl/source/reusable_events.cpp	Stores the property on event implementations.
sycl/source/detail/event_impl.hpp	Adds low-power event state.
sycl/source/detail/event_impl.cpp	Chains the UR synchronization descriptor.
sycl/include/sycl/ext/oneapi/experimental/reusable_events.hpp	Exposes the new property.
sycl/include/sycl/detail/properties/property.hpp	Registers its property kind.
sycl/doc/extensions/experimental/sycl_ext_oneapi_reusable_events.asciidoc	Documents the property.

Review details

• Files reviewed: 23/23 changed files
• Comments generated: 1
• Review effort level: Balanced

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[guangyey]

Just a question: do we still need https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/sycl_ext_intel_event_mode.asciidoc

[ldorau]

@dyniols Source Checks failed - please fix it.

[dyniols]

@dyniols Source Checks failed - please fix it.

I will. What about https://github.com/intel/llvm/actions/runs/35329623794/job/105557514508?pr=23177 I don’t think that failure is related. Since the Offload adapter is failing, and I haven’t changed anything there, as far as I understand UR.

[dyniols]

Just a question: do we still need https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/sycl_ext_intel_event_mode.asciidoc

I think with addition of low_power to reusable events extension we don't need that separate extension anymore. However I am not sure let me ask @gmlueck.

[ldorau]

@dyniols Source Checks failed - please fix it.

I will. What about https://github.com/intel/llvm/actions/runs/35329623794/job/105557514508?pr=23177 I don't think the failures are related to Offload adapter since I haven't changed anything there as far I understand UR.

I suppose you can ignore it - @lplewa, right?

[dyniols]

Okay, I think I fixed "Source Checks" but let's wait until CI is done ;)

[gmlueck]

Thanks for reminding me about sycl_ext_intel_event_mode. This makes me think we should change this property to an enum like:

namespace sycl::ext::oneapi::experimental {

enum class event_mode_enum { none, low_power };

struct event_mode {
  event_mode(event_mode_enum mode);
};
using event_mode_key = event_mode;

}

This will let us easily add other modes in the future that correspond to ZE_EVENT_SYNC_MODE_FLAG_SIGNAL_INTERRUPT or ZE_EVENT_SYNC_MODE_FLAG_EXTERNAL_INTERRUPT_WAIT should we find a need.

Do you have any concerns with that, @guangyey?

I agree that we can eventually deprecate / remove sycl_ext_intel_event_mode. However, let's wait for sycl_ext_oneapi_reusable_events to be fully implemented first.

[guangyey]

I have no strong preference. For PyTorch, lower_power should be sufficient.

[gmlueck]

If you have no strong preference, let's go with the event_mode and enumeration.

[guangyey]

event_mode_enum::none means regular wait, right? So, we could write code like this:

sycl::event createEvent(bool timing, bool low_power) {
    return syclex::make_event(context, syclex::properties{
              syclex::enable_profiling{enable_timing_},
              syclex::event_mode{low_power ? event_mode_enum::low_power : event_mode_enum::none},
    });
}

[gmlueck]

Correct.

[dyniols]

Ok, I will change it to the event_mode and enumeration.

[guangyey]

Thanks. It's a good design for our use.

[dyniols]

Moving to draft since I need re-work the changes to apply #23177 (comment)