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* [gcc/devel/omp/gcc-12] libgomp.texi: Reverse-offload updates
@ 2023-02-01 14:29 Tobias Burnus
0 siblings, 0 replies; only message in thread
From: Tobias Burnus @ 2023-02-01 14:29 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:6b611f1b3ca5edae8e3500209cea82128b2dc594
commit 6b611f1b3ca5edae8e3500209cea82128b2dc594
Author: Tobias Burnus <tobias@codesourcery.com>
Date: Wed Feb 1 15:29:11 2023 +0100
libgomp.texi: Reverse-offload updates
libgomp/
* libgomp.texi (5.0 Impl. Status): Update 'requires' and 'ancestor'.
(GCN): Add item about 'omp requires'.
(nvptx): Likewise; add item about reverse offload.
(cherry picked from commit eda38850a7980d78d966a39b58961349bea7c984)
Diff:
---
libgomp/ChangeLog.omp | 9 +++++++++
libgomp/libgomp.texi | 26 +++++++++++++++++++-------
2 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/libgomp/ChangeLog.omp b/libgomp/ChangeLog.omp
index 3d1cb16348a..75a47a77ed7 100644
--- a/libgomp/ChangeLog.omp
+++ b/libgomp/ChangeLog.omp
@@ -1,3 +1,12 @@
+2023-02-01 Tobias Burnus <tobias@codesourcery.com>
+
+ Backported from master:
+ 2023-02-01 Tobias Burnus <tobias@codesourcery.com>
+
+ * libgomp.texi (5.0 Impl. Status): Update 'requires' and 'ancestor'.
+ (GCN): Add item about 'omp requires'.
+ (nvptx): Likewise; add item about reverse offload.
+
2023-02-01 Tobias Burnus <tobias@codesourcery.com>
Backported from master:
diff --git a/libgomp/libgomp.texi b/libgomp/libgomp.texi
index 966af076f31..dc3da5a84e8 100644
--- a/libgomp/libgomp.texi
+++ b/libgomp/libgomp.texi
@@ -192,8 +192,8 @@ The OpenMP 4.5 specification is fully supported.
env variable @tab Y @tab
@item Nested-parallel changes to @emph{max-active-levels-var} ICV @tab Y @tab
@item @code{requires} directive @tab P
- @tab complete but no non-host devices provides @code{unified_address},
- @code{unified_shared_memory} or @code{reverse_offload}
+ @tab complete but no non-host devices provides @code{unified_address} or
+ @code{unified_shared_memory}
@item @code{teams} construct outside an enclosing target region @tab Y @tab
@item Non-rectangular loop nests @tab P @tab Full support for C/C++, partial for Fortran
@item @code{!=} as relational-op in canonical loop form for C/C++ @tab Y @tab
@@ -228,7 +228,7 @@ The OpenMP 4.5 specification is fully supported.
@item @code{allocate} clause @tab P @tab Initial support
@item @code{use_device_addr} clause on @code{target data} @tab Y @tab
@item @code{ancestor} modifier on @code{device} clause
- @tab Y @tab See comment for @code{requires}
+ @tab Y @tab Host fallback with GCN devices
@item Implicit declare target directive @tab Y @tab
@item Discontiguous array section with @code{target update} construct
@tab N @tab
@@ -288,7 +288,7 @@ The OpenMP 4.5 specification is fully supported.
@code{append_args} @tab N @tab
@item @code{dispatch} construct @tab N @tab
@item device-specific ICV settings with environment variables @tab Y @tab
-@item @code{assume} directive @tab Y @tab
+@item @code{assume} and @code{assumes} directives @tab Y @tab
@item @code{nothing} directive @tab Y @tab
@item @code{error} directive @tab Y @tab
@item @code{masked} construct @tab Y @tab
@@ -351,7 +351,7 @@ The OpenMP 4.5 specification is fully supported.
to address of matching mapped list item per 5.1, Sect. 2.21.7.2 @tab N @tab
@item For Fortran, diagnose placing declarative before/between @code{USE},
@code{IMPORT}, and @code{IMPLICIT} as invalid @tab N @tab
-@item Optional comma beween directive and clause in the @code{#pragma} form @tab Y @tab
+@item Optional comma between directive and clause in the @code{#pragma} form @tab Y @tab
@item @code{indirect} clause in @code{declare target} @tab N @tab
@item @code{device_type(nohost)}/@code{device_type(host)} for variables @tab N @tab
@end multitable
@@ -3959,7 +3959,7 @@ same context.
@section First invocation: OpenACC library API
In this second use case (see below), a function in the OpenACC library is
-called prior to any of the functions in the CUBLAS library. More specificially,
+called prior to any of the functions in the CUBLAS library. More specifically,
the function @code{acc_set_device_num()}.
In the use case presented here, the function @code{acc_set_device_num()}
@@ -4451,6 +4451,9 @@ The implementation remark:
@item I/O within OpenMP target regions and OpenACC compute regions is supported
using the C library @code{printf} functions and the Fortran
@code{print}/@code{write} statements.
+@item OpenMP code that has a requires directive with @code{unified_address},
+ @code{unified_shared_memory} or @code{reverse_offload} will remove
+ any GCN device from the list of available devices (``host fallback'').
@end itemize
@@ -4491,7 +4494,7 @@ which caches the JIT in the user's directory (see CUDA documentation; can be
tuned by the environment variables @code{CUDA_CACHE_@{DISABLE,MAXSIZE,PATH@}}.
Note: While PTX ISA is generic, the @code{-mptx=} and @code{-march=} commandline
-options still affect the used PTX ISA code and, thus, the requirments on
+options still affect the used PTX ISA code and, thus, the requirements on
CUDA version and hardware.
The implementation remark:
@@ -4504,6 +4507,15 @@ The implementation remark:
@item Compilation OpenMP code that contains @code{requires reverse_offload}
requires at least @code{-march=sm_35}, compiling for @code{-march=sm_30}
is not supported.
+@item For code containing reverse offload (i.e. @code{target} regions with
+ @code{device(ancestor:1)}), there is a slight performance penalty
+ for @emph{all} target regions, consisting mostly of shutdown delay
+ Per device, reverse offload regions are processed serially such that
+ the next reverse offload region is only executed after the previous
+ one returned.
+@item OpenMP code that has a requires directive with @code{unified_address}
+ or @code{unified_shared_memory} will remove any nvptx device from the
+ list of available devices (``host fallback'').
@end itemize
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