libOpenCL(7)
============
Vincent Danjean <Vincent.Danjean@ens-lyon.org>
:Author Initials: VD
:revdate: 2015-06-08
:footer-style: revdate
:toc:
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NAME
----
libOpenCL, libOpenCL.so - OCL-ICD implementation of OpenCL ICD loader

DESCRIPTION
-----------
`libOpenCL.so` is the library linked by OpenCL programs. It does not contains
any OpenCL implementation itself, but merly act as a dispatcher to real OpenCL
implementations provided as OpenCL Installable Client Driver (ICD).
An ICD loader should be able to load ICDs provided by any vendors.

According to OpenCL specifications from Khronos (see [Khronos]), the ICD Loader
looks for files into '`/etc/OpenCL/vendors/`' directory and, for each file
whose name ends with '`.icd`', the ICD Loader loads with **dlopen**(3) the
shared library whose name is on the first line of the '`.icd`' file.

Shared library name in ".icd" files can have its path, or it can be a plain
filename. In the latter case, the ICD shared library will be look for into the
standard dynamic loader paths.

ENVIRONMENT
-------------
Some environment variables can be used modify the default behavior of
libOpenCL.

*OCL_ICD_VENDORS*::
This variable allows one to change the way ICD are searched on the system.
Several cases are considered:

a. if *$OCL_ICD_VENDORS* is a directory path, then this path replaces the
  "/etc/OpenCL/vendors" path in the standard behavior: the loader will use the
  '`.icd`' files in this directory;
b. else, if *$OCL_ICD_VENDORS* ends with '`.icd`', libOpenCL.so will only load
  the ICD whose shared library name is wrote into the specified ".icd"
  file;
  +
  If there is no slash into
  *$OCL_ICD_VENDORS*, libOpenCL.so will first try to use
  '`/etc/OpenCL/vendors/`'*$OCL_ICD_VENDORS*. If this fail, it uses
  *$OCL_ICD_VENDORS* (as a relative or absolute file name path).
c. else libOpenCL.so will try to load *$OCL_ICD_VENDORS* as the ICD shared
  library itself (i.e. to load it directly with **dlopen**(3)).

*OCL_ICD_ASSUME_ICD_EXTENSION*::
If set, contrary the Khronos specification, the loader will not check that
the loaded ICDs declare the `cl_khr_icd` extension. You may need to define
this environment variable if you are using the Intel ICD together with
*optirun*(1). Else, a bug into the Intel ICD will make the application crash.

*OCL_ICD_PLATFORM_SORT*::
Allows one to choose the way platforms are sorted when presented to programs
through **clGetPlatformIDs**(3). Current provided algorithms are:

* *devices*: first, list platforms that support most GPU, then most CPU then
  most accelerators. If *OCL_ICD_PLATFORM_SORT* is not set or set to an
  unknown value, this algorithm is used.
* *none*: no sort is done and the order can very at each run.

*OCL_ICD_DEFAULT_PLATFORM*::
Number of the platform to choose as defaut platform. Note that using this
environment variable without specifying a sort algorithm for platforms
is not really useful.

*OCL_ICD_DEBUG*::
+
--
If ocl-icd has been compiled with debug support, you can set this environment
variable to a value where each bit display some kind of informations. Defined
values are:

* *1*: warnings (enabled by default if debug support is present and
  *OCL_ICD_DEBUG* is not set)
* *2*: informative messages
* *4*: entering/exiting for some OpenCL functions
* *8*: dump of the internal structure of loaded ICDs

*OCL_ICD_DEBUG* is mainly useful for ocl-icd development itself and/or for ICD
development.
--

SEE ALSO
--------
http://www.khronos.org/registry/cl/[Khronos OpenCL registry website]
