Lesson_Materials/Device_Discovery/index.html

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					<div class="trademarks">SYCL and the SYCL logo are trademarks of the Khronos Group Inc.</div>
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						## Device Discovery
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					## Learning Objectives
					* Learn about the SYCL system topology and how to traverse it
					* Learn how to query information about a platform or device
					* Learn how to select a device; both manually and using device selectors
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						#### SYCL System Topology
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						* A SYCL application can execute work across a range of different heterogeneous devices.
						* The devices that are available in any given system are determined at runtime through topology discovery.
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						#### Platforms and devices
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						* The SYCL runtime will discover a set of platforms that are available in the system.
						  * Each platform represents a backend implementation such as Intel OpenCL or Nvidia PTX.
						* The SYCL runtime will also discover all the devices available for each of those platforms.
						  * CPU, GPU, FPGA, and other kinds of accelerators.
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						![SYCL](../common-revealjs/images/devices-1.png "SYCL-Devices")
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						#### Platform and device classes
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						* Platforms and devices are represented by the `platform` and `device` classes respectively.
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							![SYCL](../common-revealjs/images/devices-1.png "SYCL-Devices")
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				</section>
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						#### Querying the topology
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						* In SYCL there are two ways to query a system’s topology.
						  * The topology can be manually queried and iterated over via APIs of the platform and device classes .
						  * The topology can be automatically queried and iterated over using a use  specified heuristic by a device selector object.
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						#### Querying manually
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							<code><pre>
auto platforms = platform::get_platforms();

							</code></pre>
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						    ![SYCL](../common-revealjs/images/devices-5.png "SYCL-Devices")
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							* The platform class provides the static function `get_platforms`.
							  * It retrieves a vector of all available platforms in the system.
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						#### Querying manually
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							<code><pre>
auto intelDevices = intelPlatform.get_devices();

							</code></pre>
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						    ![SYCL](../common-revealjs/images/devices-6.png "SYCL-Devices")
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							* The platform class provides the member function
							`get_devices` that returns a vector of all devices
							associated with that platform.
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						#### Querying manually
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							<code><pre>
auto devices = device::get_devices();

							</code></pre>
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						    ![SYCL](../common-revealjs/images/devices-7.png "SYCL-Devices")
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							* The device class also provides the static
							function `get_devices` that returns a vector of all
							available devices in the system.
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				</section>
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						#### Querying with a device selector
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					<div class="container">
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							![Device Topology](../common-revealjs/images/topology-1.png "Device-Topology")
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							* To simplify the process of traversing the system topology SYCL provides device selectors.
							* A device selector is is a callable C++ object which defines a heuristic for scoring devices.
							* SYCL provides a number of standard device selectors, e.g. `default_selector_v`, `gpu_selector_v`, etc.
							* Users can also create their own device selectors.
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						#### Querying with a device selector
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							<code><pre>
auto gpuDevice = device(gpu_selector_v); 
							</code></pre>
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						    ![Device Topology](../common-revealjs/images/topology-1.png "Device-Topology")
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							* A device selector takes a parameter of type `const device &` and gives it a "score".
							* Used to query all devices and return the one with the highest "score".
							* A device with a negative score will never be chosen.
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				</section>
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						#### Querying the topology using a device selector
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							<code><pre>
auto chosenDevice = device();
auto chosenDevice = device(default_selector_v);
							</code></pre>
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						    ![Device Topology](../common-revealjs/images/topology-1.png "Device-Topology")
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							* The `default_selector_v` is a standard device selector.
							* Chooses a device based on an implementation defined heuristic.
							* A default constructed device or platform will use this selector.
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						#### Creating a custom device selector
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						<code><pre>
<mark>int my_gpu_selector(const device& dev) {</mark>

<mark>}</mark>
						</code></pre>
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						* A device selector can be any callable object.
						* A device selector must have a function call operator which takes a reference to a device.
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				</section>
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						#### Creating a custom device selector
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						<code><pre>
int my_gpu_selector(const device& dev) {
  <mark>if (dev.is_gpu()){</mark>
    <mark>return 1;</mark>
  <mark>}</mark>
  <mark>else {</mark>
    <mark>return -1;</mark>
  <mark>}</mark>
}
						</code></pre>
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						* The body of the function call operator defines the heuristic for selecting devices
						* This is where you write the logic for scoring each device
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						#### Creating a custom device selector
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					<div class="container">
						<code><pre>
int my_gpu_selector(const device& dev) {
  if (dev.is_gpu()){
    return 1;
  }
  else {
    return -1;
  }
}

int main(int argc, char *argv[]) {
  <mark>auto gpuQueue = queue{my_gpu_selector};</mark>

}
						</code></pre>
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						* Now that there is a device selector that chooses a specific device we can use that to construct a queue.
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						#### Platform/device info
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							<code><pre>
auto plt = dev.get_platform();
auto platformName
  = dev.get_info&lt;info::device::name&gt;();
							</code></pre>
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						    ![SYCL](../common-revealjs/images/topology-2.png "SYCL-Devices")
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							* Information about platforms and devices can be queried using the template member function `get_info`.
							* The info that you are querying is specified by the template parameter.
							* You can also query a device for its associated platform with the `get_platform` member function.
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						#### Aspects
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							<code><pre>
bool supportsFp16 = dev.has(aspect::fp16);
							</code></pre>
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							* Capabilities of a device or platform are
							represented by aspects.
							* These can be queried via the `has` member
							function.
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				</section>
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				<section>
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						## Questions
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						#### Exercise
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						Code_Exercises/Device_Discovery/source
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						Create your own device selector that chooses the device in your system that you would like to target.
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				</section>
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