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<title>clSVMAlloc</title>
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<div class="refentry">
<a id="id-1"></a>
<div class="titlepage"></div>
<div xmlns="" class="refnamediv">
<a xmlns="http://www.w3.org/1999/xhtml" id="clSVMAlloc"></a>
<h1>
clSVMAlloc
</h1>
<p>
Allocates a shared virtual memory (SVM) buffer that can be shared by the host and all devices in an OpenCL context that support shared virtual memory.
</p>
</div>
<div class="refsynopsisdiv">
<h2></h2>
<div class="funcsynopsis">
<table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
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<td>
<code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
<a class="link" href="abstractDataTypes.html" target="pagedisplay">void</a> <strong class="fsfunc"> * clSVMAlloc</strong>
(</code>
<td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_context</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">context</var>, </td>
</td>
</tr>
<tr valign="top">
<td> </td>
<td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="enums.html#cl_svm_mem_flags" target="pagedisplay">cl_svm_mem_flags</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">flags</var>, </td>
</tr>
<tr valign="top">
<td> </td>
<td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">size</var>, </td>
</tr>
<tr valign="top">
<td> </td>
<td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">cl_uint</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">alignment</var><code>)</code></td>
</tr>
</table>
</div>
</div>
<div class="refsect1">
<a id="parameters"></a>
<h2>Parameters</h2>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term">
<code class="varname">context</code>
</span>
</dt>
<dd>
<p>A valid OpenCL context used to create the SVM buffer.</p>
</dd>
<dt>
<span class="term"> <code class="varname">flags</code> </span>
</dt>
<dd>
<p>
A bit-field that is used to specify
allocation and usage information. The following
table describes the possible values for <code class="varname">flags</code>.
</p>
<div class="informaltable">
<table class="informaltable" border="1">
<colgroup>
<col align="left" class="col1" />
<col align="left" class="col2" />
</colgroup>
<thead>
<tr>
<th align="left">cl_svm_mem_flags</th>
<th align="left">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">
<code class="constant">CL_MEM_READ_WRITE</code>
</td>
<td align="left">
This flag specifies that the SVM buffer will be read
and written by a kernel. This is the default.
</td>
</tr>
<tr>
<td align="left">
<code class="constant">CL_MEM_WRITE_ONLY</code>
</td>
<td align="left">
<p>
This flag specifies that the SVM buffer will be written
but not read by a kernel.
</p>
<p>
Reading from a SVM buffer created with
<code class="constant">CL_MEM_WRITE_ONLY</code> inside a kernel is undefined.
</p>
<p>
<code class="constant">CL_MEM_READ_WRITE</code> and
<code class="constant">CL_MEM_WRITE_ONLY</code> are mutually exclusive.
</p>
</td>
</tr>
<tr>
<td align="left">
<code class="constant">CL_MEM_READ_ONLY</code>
</td>
<td align="left">
<p>
This flag specifies that the SVM buffer object is a
read-only memory object when used inside a kernel.
</p>
<p>
Writing to a SVM buffer created with
<code class="constant">CL_MEM_READ_ONLY</code> inside a kernel is undefined.
</p>
<p>
<code class="constant">CL_MEM_READ_WRITE</code> or <code class="constant">CL_MEM_WRITE_ONLY</code> and
<code class="constant">CL_MEM_READ_ONLY</code> are mutually exclusive.
</p>
</td>
</tr>
<tr>
<td align="left">
<code class="constant">CL_MEM_SVM_FINE_GRAIN_BUFFER</code>
</td>
<td align="left">
This specifies that the application wants the OpenCL
implementation to do a fine-grained allocation.
</td>
</tr>
<tr>
<td align="left">
<code class="constant">CL_MEM_SVM_ATOMICS</code>
</td>
<td align="left">
This flag is valid only if
<code class="constant">CL_MEM_SVM_FINE_GRAIN_BUFFER</code> is specified in
<code class="varname">flags</code>. It is used to indicate that SVM atomic
operations can control visibility of memory accesses
in this SVM buffer.
</td>
</tr>
</tbody>
</table>
</div>
</dd>
<dt>
<span class="term">
<code class="varname">size</code>
</span>
</dt>
<dd>
<p>The size in bytes of the SVM buffer to be allocated.</p>
</dd>
<dt>
<span class="term">
<code class="varname">alignment</code>
</span>
</dt>
<dd>
<p>
The minimum alignment in bytes that is required for
the newly created buffer’s
memory region. It must be a power of two up to the
largest data type supported by the OpenCL
device. For the full profile, the largest data type
is <span class="type">long16</span>. For the embedded profile, it is
<span class="type">long16</span> if the device supports 64-bit
integers; otherwise it is <span class="type">int16</span>. If
alignment is 0, a
default alignment will be used that is equal to
the size of largest data type supported by the
OpenCL implementation.
</p>
</dd>
</dl>
</div>
</div>
<div class="refsect1">
<a id="notes"></a>
<h2>Notes</h2>
<p>
If <code class="constant">CL_MEM_SVM_FINE_GRAIN_BUFFER</code> is not
specified, the buffer can be created as a coarse
grained SVM allocation. Similarly, if <code class="constant">CL_MEM_SVM_ATOMICS</code>
is not specified, the buffer can be
created without support for SVM atomic
operations (refer to the OpenCL C++ kernel language and IL specifications).
</p>
<p>
Calling <code class="function">clSVMAlloc</code> does not itself
provide consistency for the shared memory region. When
the host can’t use the SVM atomic operations, it
must rely on OpenCL’s guaranteed memory
consistency at synchronization points.
</p>
<p>
For SVM to be used efficiently, the host and any
devices sharing a buffer containing virtual
memory pointers should have the same endianness.
If the context passed to <code class="function">clSVMAlloc</code> has
devices with mixed endianness and the OpenCL
implementation is unable to implement SVM
because of that mixed endianness,
<code class="function">clSVMAlloc</code> will fail and return NULL.
</p>
<p>
Although SVM is generally not supported for image objects,
<a class="citerefentry" href="clCreateImage.html"><span class="citerefentry"><span class="refentrytitle">clCreateImage</span></span></a>
may create an image from a buffer (a 1D image from a buffer
or a 2D image from buffer) if the buffer specified
in its image description parameter is a SVM
buffer. Such images have a linear memory
representation so their memory can be
shared using SVM. However, fine grained sharing and
atomics are not supported for image reads and writes in a kernel.
</p>
<p>
If <a class="citerefentry" href="clCreateBuffer.html"><span class="citerefentry"><span class="refentrytitle">clCreateBuffer</span></span></a>
is called with a pointer returned by
<code class="function">clSVMAlloc</code> as its
<code class="varname">host_ptr</code> argument, and
<code class="constant">CL_MEM_USE_HOST_PTR</code> is set in its <code class="varname">flags</code> argument,
<a class="citerefentry" href="clCreateBuffer.html"><span class="citerefentry"><span class="refentrytitle">clCreateBuffer</span></span></a>
will succeed and return a
valid non-zero buffer object as long as the <code class="varname">size</code>
argument to
<a class="citerefentry" href="clCreateBuffer.html"><span class="citerefentry"><span class="refentrytitle">clCreateBuffer</span></span></a>
is no larger than the
<code class="varname">size</code> argument passed in the original
<code class="function">clSVMAlloc</code> call. The new buffer object returned has the
shared memory as the underlying storage. Locations in
the buffer's underlying shared memory
can be operated on using atomic operations to the device's
level of support as defined in the
memory model.
</p>
</div>
<div class="refsect1">
<a id="errors"></a>
<h2>Errors</h2>
<p>
Returns a valid non-NULL shared virtual memory address if the SVM buffer is
successfully allocated. Otherwise, like malloc, it returns a NULL pointer
value. <code class="function">clSVMAlloc</code> will fail if:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem" style="list-style-type: disc"><code class="varname">context</code> is not a valid context.
</li>
<li class="listitem" style="list-style-type: disc"><code class="varname">flags</code> does not contain
<code class="constant">CL_MEM_SVM_FINE_GRAIN_BUFFER</code> but does contain
<code class="constant">CL_MEM_SVM_ATOMICS</code>.
</li>
<li class="listitem" style="list-style-type: disc">
Values specified in <code class="varname">flags</code> do not follow
rules described for supported values in the table above.
</li>
<li class="listitem" style="list-style-type: disc"><code class="constant">CL_MEM_SVM_FINE_GRAIN_BUFFER</code> or
<code class="constant">CL_MEM_SVM_ATOMICS</code> is specified in
<code class="varname">flags</code> and these are not supported
by at least one device in <code class="varname">context</code>.
</li>
<li class="listitem" style="list-style-type: disc">
The values specified in <code class="varname">flags</code> are
not valid i.e. don’t match those defined in the table above.
</li>
<li class="listitem" style="list-style-type: disc"><code class="varname">size</code> is 0 or &gt; <code class="constant">CL_DEVICE_MAX_MEM_ALLOC_SIZE</code>
value for any device in <code class="varname">context</code>.
</li>
<li class="listitem" style="list-style-type: disc"><code class="varname">alignment</code> is not a power of two
or the OpenCL implementation cannot support the
specified alignment for at least one device in <code class="varname">context</code>.
</li>
<li class="listitem" style="list-style-type: disc">
There was a failure to allocate resources.
</li>
</ul>
</div>
</div>
<div class="refsect1">
<a id="specification"></a>
<h2>Specification</h2>
<p>
<img src="pdficon_small1.gif" />
<a href="https://www.khronos.org/registry/cl/specs/opencl-2.1.pdf#page=175" target="OpenCL Spec">OpenCL Specification</a>
</p>
</div>
<div class="refsect1">
<a id="seealso"></a>
<h2>Also see</h2>
<p>
<a class="citerefentry" href="clSVMFree.html"><span class="citerefentry"><span class="refentrytitle">clSVMFree</span></span></a>,
<a class="citerefentry" href="sharedVirtualMemory.html"><span class="citerefentry"><span class="refentrytitle">Shared Virtual Memory Functions</span></span></a>
</p>
</div>
<div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
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