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<!doctype html>
<html>
<head>
<meta charset="utf-8"/>
<link rel="stylesheet" href="../../Static/css/reveal.css"/>
<link rel="stylesheet" href="../../Static/css/theme/white.css"/>
<link rel="stylesheet" href="../../Static/css/custom.css"/>
<link rel="stylesheet" href="../../Static/css/atom-one-light.css"/>
<script src="../../node_modules/reveal.js/dist/reveal.js" defer></script>
<script src="../../node_modules/reveal.js/dist/plugin/markdown.js" defer></script>
<script src="../../node_modules/reveal.js/dist/plugin/highlight.js" defer></script>
<script src="../../node_modules/reveal.js/dist/plugin/notes.js" defer></script>
<script src="../../js/plugins/merge-html.js" defer></script>
<script src="../../js/setup.js" defer></script>
</head>
<body>
<div class="reveal">
<div class="slides">
<!--Slide 1-->
<section class="hbox">
<div class="hbox" data-markdown>
## Introduction to USM
</div>
</section>
<!--Slide 2-->
<section class="hbox" data-markdown>
## Learning Objectives
* Learn about the USM data management model
* Learn about the benefits of USM and when to use it
* Learn about the variations of USM
* Learn about the kinds of USM memory allocations
</section>
<!--Slide 3-->
<section>
<div class="hbox" data-markdown>
#### What is USM?
</div>
<div class="container" data-markdown>
Unified shared memory (USM) provides a pointer-based data management model
</div>
<div class="container" data-markdown>
* Unified virtual address space
* Pointer-based structures
* Explicit memory management
* Shared memory allocations
</div>
</section>
<!--Slide 4-->
<section>
<div class="hbox" data-markdown>
#### Unified virtual address space
</div>
<div class="container">
<div class="col" data-markdown>
</div>
<div class="col" data-markdown>
* USM memory allocations return pointers which are consistent between the host application and kernel functions on a device
* Pointer-based API more familiar to C or C++ programmers
</div>
</div>
</section>
<!--Slide 5-->
<section>
<div class="hbox" data-markdown>
#### Pointer based structures
</div>
<div class="container">
<div class="col" data-markdown>
</div>
<div class="col" data-markdown>
* Data is moved between the host and device(s) in a span of memory in bytes
* Pointers within that region of memory can freely point to any other address in that region
* Easier to port existing C or C++ code to use SYCL
</div>
</div>
</section>
<!--Slide 6-->
<section>
<div class="hbox" data-markdown>
#### Explicit memory management
</div>
<div class="container">
<div class="col" data-markdown>
</div>
<div class="col" data-markdown>
* Memory is allocated and data is moved using explicit routines
* The SYCL runtime will not perform any data dependency analysis, dependencies between commands must be managed manually
</div>
</div>
</section>
<!--Slide 7-->
<section>
<div class="hbox" data-markdown>
#### Shared memory allocations
</div>
<div class="container">
<div class="col" data-markdown>
</div>
<div class="col" data-markdown>
* Some platforms will support variants of USM where memory allocations share the same memory region between the host and device(s)
* No explicit routines are required to move the data between the host and device(s)
</div>
</div>
</section>
<!--Slide 8-->
<section>
<div class="hbox" data-markdown>
#### USM allocation types
</div>
<div class="container" data-markdown>
USM has three different kinds of memory allocation
</div>
<div class="container" data-markdown>
* A **host** allocation is allocated in host memory
* A **device** allocation is allocation in device memory
* A **shared** allocation is allocated in shared memory and can migrate back and forth
</div>
</section>
<!--Slide 9-->
<section>
<div class="hbox" data-markdown>
#### USM variants
</div>
<div class="container" data-markdown>
USM has four variants which a platform can support with varying levels of support.
Only Explicit USM is guraranteed to be available, with the others optional.
</div>
<div class="container" data-markdown>
| | Explicit USM | Restricted USM | Concurrent USM | System USM |
|------------------------|--------------|----------------|----------------|------------|
| Consistent pointers | ✓ | ✓ | ✓ | ✓ |
| Pointers in structures | ✓ | ✓ | ✓ | ✓ |
| Explicit data movement | ✓ | ✓ | ✓ | ✓ |
| Shared allocations | ✗ | ✓ | ✓ | ✓ |
| Concurrent access | ✗ | ✗ | ✓ | ✓ |
| System allocations | ✗ | ✗ | ✗ | ✓ |
</div>
</section>
<!--Slide 10-->
<section>
<div class="hbox" data-markdown>
#### Querying for support
</div>
<div class="container" data-markdown>
Each SYCL platform and its device(s) will support
different variants of USM and different kinds of memory allocation
</div>
<pre><code class="language-cpp" data-line-numbers>if (dev.has(sycl::aspect::usm_device_allocations))</code></pre>
</section>
<!--Slide 12-->
<section>
<div class="hbox" data-markdown>
## Questions
</div>
</section>
<!--Slide 13-->
<section>
<div class="hbox" data-markdown>
#### Exercise
</div>
<div class="container" data-markdown>
Code_Exercises/Introduction_to_USM/source
</div>
<div class="container" data-markdown>
Implement a device selector that chooses a device in your system which supports explicit USM and device allocations
</div>
</section>
</div>
</div>
</body>
</html>