[SYCL] Support sycl_ext_oneapi_platform_device_index #20758
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@vinser52 @intel/llvm-reviewers-runtime could you take a look please. |
| size_t device::ext_oneapi_index_within_platform() const { | ||
| auto devices = get_platform().get_devices(); | ||
| auto it = std::find(devices.begin(), devices.end(), *this); | ||
| if (it == devices.end()) | ||
| throw sycl::exception(sycl::make_error_code(errc::invalid), | ||
| "this device is not a root device"); | ||
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| size_t index = std::distance(devices.begin(), it); | ||
| return index; | ||
| } |
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The goal of the extension is to get the device index in an efficient way. Do we really need to scan the vector returned by platform::get_devices() everytime? Can we cache the result of the scan on the first call to the ext_oneapi_index_within_platform and return the cached value on all subsequent calls?
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Yeah, looks like I've implemented what we wanted to avoid.
Anyways, with cache the first run is still expensive. I'd like to hear from @gmlueck - could you please tell, what was the idea regarding improving the efficiency? To use L0 and OCL calls?
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Anyways, with cache the first run is still expensive.
Devices are only created once, together with the platform I believe. Maybe we could store the index inside the device_impl when we create the platforms and their devices?
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Yes, this is what I had in mind. Store each device's index when the device_impl is first created. Then, we can retrieve the index in O(1) time.
For the reverse operation (index to device), I assume we already store a vector of devices for each platform? If so, converting from index to device should be a simple index operation into this vector.
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https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_platform_device_index.asciidoc