Now that the reverse-offload patch is (nearly) in:
On 07.12.22 09:08, Tobias Burnus wrote:
On 06.12.22 08:45, Tobias Burnus wrote:
* As follow-up, libgomp.texi must be updated
Slight update to that uncommitted patch: I extended the nvptx entry to
state that only one reverse-offload region runs at a given time.
OK?
Tobias
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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.
libgomp/libgomp.texi | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/libgomp/libgomp.texi b/libgomp/libgomp.texi
index b6c1ed714ce..f95e82fc8aa 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 Y @tab
@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
@@ -4456,6 +4456,9 @@ The implementation remark:
@item I/O within OpenMP target regions and OpenACC parallel/kernels 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
@@ -4507,6 +4510,15 @@ 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 penality
+ for @emph{all} target regions, consisting mostly of shutdown delay
+ Per device, reverse offload regions are processed serial such that
+ the next reverse offload region is only executed after the previous
+ one returns.
+@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
