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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<link rel="stylesheet" href="../common-revealjs/css/reveal.css">
<link rel="stylesheet" href="../common-revealjs/css/theme/white.css">
<link rel="stylesheet" href="../common-revealjs/css/custom.css">
<script>
// This is needed when printing the slides to pdf
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match( /print-pdf/gi ) ? '../common-revealjs/css/print/pdf.css' : '../common-revealjs/css/print/paper.css';
document.getElementsByTagName( 'head' )[0].appendChild( link );
</script>
<script>
// This is used to display the static images on each slide,
// See global-images in this html file and custom.css
(function() {
if(window.addEventListener) {
window.addEventListener('load', () => {
let slides = document.getElementsByClassName("slide-background");
if (slides.length === 0) {
slides = document.getElementsByClassName("pdf-page")
}
// Insert global images on each slide
for(let i = 0, max = slides.length; i < max; i++) {
let cln = document.getElementById("global-images").cloneNode(true);
cln.removeAttribute("id");
slides[i].appendChild(cln);
}
// Remove top level global images
let elem = document.getElementById("global-images");
elem.parentElement.removeChild(elem);
}, false);
}
})();
</script>
</head>
<body>
<div class="reveal">
<div class="slides">
<div id="global-images" class="global-images">
<img src="../common-revealjs/images/sycl_academy.png" />
<img src="../common-revealjs/images/sycl_logo.png" />
<img src="../common-revealjs/images/trademarks.png" />
</div>
<!--Slide 1-->
<section class="hbox">
<div class="hbox" data-markdown>
## Device Discovery
</div>
</section>
<!--Slide 2-->
<section class="hbox" data-markdown>
## 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
</section>
<!--Slide 3-->
<section>
<div class="hbox" data-markdown>
#### SYCL System Topology
</div>
<div class="container" data-markdown>
* 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.
</div>
</section>
<!--Slide 4-->
<section>
<div class="hbox" data-markdown>
#### Platforms and devices
</div>
<div class="container" data-markdown>
* 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.
</div>
<div class="col" data-markdown>
</div>
</section>
<!--Slide 5-->
<!--Slide 6-->
<section>
<div class="hbox" data-markdown>
#### Platform and device classes
</div>
<div class="container" data-markdown>
* Platforms and devices are represented by the `platform` and `device` classes respectively.
</div>
<div class="container">
<div class="col" data-markdown>
</div>
</div>
<!--Slide 7-->
</section>
<section class="hbox">
<div class="hbox" data-markdown>
#### Querying the topology
</div>
<div class="hbox" data-markdown>
* 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.
</div>
</section>
<!--Slide 8-->
<section>
<div class="hbox" data-markdown>
#### Querying manually
</div>
<div class="container">
<div class="col-left-1">
<code><pre>
auto platforms = platform::get_platforms();
</code></pre>
</div>
<div class="col-right-1" data-markdown>
</div>
</div>
<div class="smaller-size-font" data-markdown>
* The platform class provides the static function `get_platforms`.
* It retrieves a vector of all available platforms in the system.
</div>
</section>
<!--Slide 9-->
<section>
<div class="hbox" data-markdown>
#### Querying manually
</div>
<div class="container">
<div class="col-left-1">
<code><pre>
auto intelDevices = intelPlatform.get_devices();
</code></pre>
</div>
<div class="col-right-1" data-markdown>
</div>
</div>
<div class="smaller-size-font" data-markdown>
* The platform class provides the member function
`get_devices` that returns a vector of all devices
associated with that platform.
</div>
</section>
<!--Slide 10-->
<section>
<div class="hbox" data-markdown>
#### Querying manually
</div>
<div class="container">
<div class="col-left-1">
<code><pre>
auto devices = device::get_devices();
</code></pre>
</div>
<div class="col-right-1" data-markdown>
</div>
</div>
<div class="smaller-size-font" data-markdown>
* The device class also provides the static
function `get_devices` that returns a vector of all
available devices in the system.
</div>
</section>
<!--Slide 11-->
<section>
<div class="hbox" data-markdown>
#### Querying with a device selector
</div>
<div class="container">
<div class="col-left-1" data-markdown>
</div>
<div class="col-right-1" data-markdown>
* 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.
</div>
</div>
</section>
<!--Slide 12-->
<section>
<div class="hbox" data-markdown>
#### Querying with a device selector
</div>
<div class="container">
<div class="col-left-1">
<code><pre>
auto gpuDevice = device(gpu_selector_v);
</code></pre>
</div>
<div class="col-right-1" data-markdown>
</div>
</div>
<div class="container" data-markdown>
* 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.
</div>
</section>
<!--Slide 13-->
<section>
<div class="hbox" data-markdown>
#### Querying the topology using a device selector
</div>
<div class="container">
<div class="col-left-1">
<code><pre>
auto chosenDevice = device();
auto chosenDevice = device(default_selector_v);
</code></pre>
</div>
<div class="col-right-1" data-markdown>
</div>
</div>
<div class="container" data-markdown>
* 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.
</div>
</section>
<!--Slide 14-->
<section>
<div class="hbox" data-markdown>
#### Creating a custom device selector
</div>
<div class="container">
<code><pre>
<mark>int my_gpu_selector(const device& dev) {</mark>
<mark>}</mark>
</code></pre>
</div>
<div class="hbox" data-markdown>
* A device selector can be any callable object.
* A device selector must have a function call operator which takes a reference to a device.
</div>
</section>
<!--Slide 15-->
<section>
<div class="hbox" data-markdown>
#### Creating a custom device selector
</div>
<div class="container">
<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>
</div>
<div class="hbox" data-markdown>
* The body of the function call operator defines the heuristic for selecting devices
* This is where you write the logic for scoring each device
</div>
</section>
<!--Slide 16-->
<section>
<div class="hbox" data-markdown>
#### Creating a custom device selector
</div>
<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>
</div>
<div class="hbox" data-markdown>
* Now that there is a device selector that chooses a specific device we can use that to construct a queue.
</div>
</section>
<!--Slide 17-->
<section>
<div class="hbox" data-markdown>
#### Platform/device info
</div>
<div class="container">
<div class="col-left-1">
<code><pre>
auto plt = dev.get_platform();
auto platformName
= dev.get_info<info::device::name>();
</code></pre>
</div>
<div class="col-right-2" data-markdown>
</div>
</div>
<div class="container" data-markdown>
* 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.
</div>
</section>
<!--Slide 18-->
<section>
<div class="hbox" data-markdown>
#### Aspects
</div>
<div class="container">
<div class="col">
<code><pre>
bool supportsFp16 = dev.has(aspect::fp16);
</code></pre>
</div>
<div class="col" data-markdown>
* Capabilities of a device or platform are
represented by aspects.
* These can be queried via the `has` member
function.
</div>
</div>
</section>
<!--Slide 19-->
<section>
<div class="hbox" data-markdown>
## Questions
</div>
</section>
<!--Slide 20-->
<section>
<div class="hbox" data-markdown>
#### Exercise
</div>
<div class="container" data-markdown>
Code_Exercises/Device_Discovery/source
</div>
<div class="container" data-markdown>
Create your own device selector that chooses the device in your system that you would like to target.
</div>
</section>
</div>
</div>
<script src="../common-revealjs/js/reveal.js"></script>
<script src="../common-revealjs/plugin/markdown/marked.js"></script>
<script src="../common-revealjs/plugin/markdown/markdown.js"></script>
<script src="../common-revealjs/plugin/notes/notes.js"></script>
<script>
Reveal.initialize({mouseWheel: true, defaultNotes: true});
Reveal.configure({ slideNumber: true });
</script>
</body>
</html>