There are two problems this patch tries to address:
1) We currently free resources in a random order wrt. plugin and
libomptarget destruction. This patch should ensure the CUDA plugin
is less fragile if something during the deinitialization goes wrong.
2) We need to support (hard) pause runtime calls eventually. This patch
allows us to free all associated resources, though we cannot
reinitialize the device yet.
Follow up patch will associate one event pool per device/context.
Differential Revision: https://reviews.llvm.org/D120089
In the OpenMC app we saw `omp target update` spending an awful lot of
time in the shadow map traversal without ever doing any update there.
There are two cases that allow us to avoid the traversal completely.
The simplest thing is that small updates cannot (reasonably) contain
an attached pointer part. The other case requires to track in the
mapping table if an entry might contain an attached pointer as part.
Given that we have a single location shadow map entries are created,
the latter is actually fairly easy as well.
Differential Revision: https://reviews.llvm.org/D113124
Atomic handling of map clauses was introduced to comply with the OpenMP
standard (see D104418). However, many apps won't need this feature which
can be costly in certain situations. To allow for applications to
opt-out we now introduce the `LIBOMPTARGET_MAP_FORCE_ATOMIC` environment
flag that voids the atomicity guarantee of the standard for map clauses
again, shifting the burden to the user.
This patch also de-duplicates the code that introduces the events used
to enforce atomicity as a cleanup.
Differential Revision: https://reviews.llvm.org/D117627
The async data movement can cause data race if the target supports it.
Details can be found in [1]. This patch tries to fix this problem by attaching
an event to the entry of data mapping table. Here are the details.
For each issued data movement, a new event is generated and returned to `libomptarget`
by calling `createEvent`. The event will be attached to the corresponding mapping table
entry.
For each data mapping lookup, if there is no need for a data movement, the
attached event has to be inserted into the queue to gaurantee that all following
operations in the queue can only be executed if the event is fulfilled.
This design is to avoid synchronization on host side.
Note that we are using CUDA terminolofy here. Similar mechanism is assumped to
be supported by another targets. Even if the target doesn't support it, it can
be easily implemented in the following fall back way:
- `Event` can be any kind of flag that has at least two status, 0 and 1.
- `waitEvent` can directly busy loop if `Event` is still 0.
My local test shows that `bug49334.cpp` can pass.
Reference:
[1] https://bugs.llvm.org/show_bug.cgi?id=49940
Reviewed By: grokos, JonChesterfield, ye-luo
Differential Revision: https://reviews.llvm.org/D104418
Johannes Doerfert