diff mbox

Document OpenACC status for GCC 6

Message ID 87h9ev0w6c.fsf@kepler.schwinge.homeip.net
State New
Headers show

Commit Message

Thomas Schwinge April 21, 2016, 4:21 p.m. UTC 
Hi!

OK to commit (something like) the following?  Should something be added
to the "News" section on <https://gcc.gnu.org/> itself?  (I don't know
the policy for that.  We didn't suggest that for GCC 5, because at that
time we described the support as a "preliminary implementation of the
OpenACC 2.0a specification"; now it's much more complete and usable.)



Grüße
 Thomas

Comments

Sandra Loosemore April 21, 2016, 6:19 p.m. UTC | #1 
On 04/21/2016 10:21 AM, Thomas Schwinge wrote:

> +	  <li>Code will be offloaded onto multiple gangs, but executes with
> +	    just one worker, and a vector length of 1.</li>

"will be" (future) vs "executes" (present).  Assuming this is all 
supposed to describe current behavior, please write consistently in the 
present tense.

> +	Typically, using the OpenACC parallel construct will give much better
> +	performance, compared to the initial support of the OpenACC kernels
> +	construct.

Here too.

My only comment on the rest of the patch is that "a kernels region" 
sounds like a mistake but I think that is the official terminology?

-Sandra the nit-picky
diff mbox

Patch

Index: htdocs/gcc-6/changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
retrieving revision 1.74
diff -u -p -r1.74 changes.html
--- htdocs/gcc-6/changes.html	19 Apr 2016 11:13:02 -0000	1.74
+++ htdocs/gcc-6/changes.html	21 Apr 2016 16:10:49 -0000
@@ -124,6 +124,52 @@  For more information, see the
 <!-- .................................................................. -->
 <h2 id="languages">New Languages and Language specific improvements</h2>
 
+<!-- <ul>
+  <li> -->Compared to GCC 5, the GCC 6 release series includes a much improved
+    implementation of the <a href="http://www.openacc.org/">OpenACC 2.0a
+      specification</a>.  Highlights are:
+    <ul>
+      <li>In addition to single-threaded host-fallback execution, offloading is
+	supported for nvptx (Nvidia GPUs) on x86_64 and PowerPC 64-bit
+	little-endian GNU/Linux host systems.  For nvptx offloading, with the
+	OpenACC parallel construct, the execution model allows for an arbitrary
+	number of gangs, up to 32 workers, and 32 vectors.</li>
+      <li>Initial support for parallelized execution of OpenACC kernels
+	constructs:
+	<ul>
+	  <li>Parallelization of a kernels region is switched on
+	    by <code>-fopenacc</code> combined with <code>-O2</code> or
+	    higher.</li>
+	  <li>Code will be offloaded onto multiple gangs, but executes with
+	    just one worker, and a vector length of 1.</li>
+	  <li>Directives inside a kernels region are not supported.</li>
+	  <li>Loops with reductions can be parallelized.</li>
+	  <li>Only kernels regions with one loop nest are parallelized.</li>
+	  <li>Only the outer-most loop of a loop nest can be parallelized.</li>
+	  <li>Loop nests containing sibling loops are not parallelized.</li>
+	</ul>
+	Typically, using the OpenACC parallel construct will give much better
+	performance, compared to the initial support of the OpenACC kernels
+	construct.
+      <li>The <code>device_type</code> clause is not supported.
+	The <code>bind</code> and <code>nohost</code> clauses are not
+	supported.  The <code>host_data</code> directive is not supported in
+	Fortran.</li>
+      <li>Nested parallelism (cf. CUDA dynamic parallelism) is not
+	supported.</li>
+      <li>Usage of OpenACC constructs inside multithreaded contexts (such as
+	created by OpenMP, or pthread programming) is not supported.</li>
+      <li>If a call to the <code>acc_on_device</code> function has a
+	compile-time constant argument, the function call evaluates to a
+	compile-time constant value only for C and C++ but not for
+	Fortran.</li>
+    </ul>
+    See the <a href="https://gcc.gnu.org/wiki/OpenACC">OpenACC</a>
+    and <a href="https://gcc.gnu.org/wiki/Offloading">Offloading</a> wiki pages
+    for further information.
+  <!-- </li>
+</ul> -->
+
 <!-- <h3 id="ada">Ada</h3> -->
 
 <h3 id="c-family">C family</h3>