[all-commits] [llvm/llvm-project] 48421a: [OpenMP] Improve ref count debug messages

[Joel E. Denny via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 48421ac441bf64ec940b13c2dee1bc1a7671e878
      https://github.com/llvm/llvm-project/commit/48421ac441bf64ec940b13c2dee1bc1a7671e878
  Author: Joel E. Denny <jdenny.ornl at gmail.com>
  Date:   2021-06-23 (Wed, 23 Jun 2021)

  Changed paths:
    M openmp/docs/design/Runtimes.rst
    M openmp/libomptarget/src/device.cpp
    M openmp/libomptarget/src/device.h
    M openmp/libomptarget/src/private.h
    M openmp/libomptarget/test/offloading/info.c

  Log Message:
  -----------
  [OpenMP] Improve ref count debug messages

For example, without this patch:

```
$ cat test.c
int main() {
  int x;
  #pragma omp target enter data map(alloc: x)
  #pragma omp target exit data map(release: x)
  ;
  return 0;
}
$ clang -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda test.c
$ LIBOMPTARGET_DEBUG=1 ./a.out |& grep 'Creating\|Mapping exists'
Libomptarget --> Creating new map entry with HstPtrBegin=0x00007ffcace8e448, TgtPtrBegin=0x00007f12ef600000, Size=4, Name=unknown
Libomptarget --> Mapping exists with HstPtrBegin=0x00007ffcace8e448, TgtPtrBegin=0x00007f12ef600000, Size=4, updated RefCount=1
```

There are two problems in this example:

* `RefCount` is not reported when a mapping is created, but it might
  be 1 or infinite.  In this case, because it's created by `omp target
  enter data`, it's 1.  Seeing that would make later `RefCount`
  messages easier to understand.
* `RefCount` is still 1 at the `omp target exit data`, but it's
  reported as `updated`.  The reason it's still 1 is that, upon
  deletions, the reference count is generally not updated in
  `DeviceTy::getTgtPtrBegin`, where the report is produced.  Instead,
  it's zeroed later in `DeviceTy::deallocTgtPtr`, where it's actually
  removed from the mapping table.

This patch makes the following changes:

* Report the reference count when creating a mapping.
* Where an existing mapping is reported, always report a reference
  count action:
    * `update suppressed` when `UpdateRefCount=false`
    * `incremented`
    * `decremented`
    * `deferred final decrement`, which replaces the misleading
      `updated` in the above example
* Add comments to `DeviceTy::getTgtPtrBegin` to explain why it does
  not zero the reference count.  (Please advise if these comments miss
  the point.)
* For unified shared memory, don't report confusing messages like
  `RefCount=` or `RefCount= updated` given that reference counts are
  irrelevant in this case.  Instead, just report `for unified shared
  memory`.
* Use `INFO` not `DP` consistently for `Mapping exists` messages.
* Fix device table dumps to print `INF` instead of `-1` for an
  infinite reference count.

Reviewed By: jhuber6, grokos

Differential Revision: https://reviews.llvm.org/D104559


  Commit: 9fa5e3280d0bfdb90e3f2823f5bc63446628682d
      https://github.com/llvm/llvm-project/commit/9fa5e3280d0bfdb90e3f2823f5bc63446628682d
  Author: Joel E. Denny <jdenny.ornl at gmail.com>
  Date:   2021-06-23 (Wed, 23 Jun 2021)

  Changed paths:
    M openmp/libomptarget/src/device.cpp
    M openmp/libomptarget/src/device.h
    M openmp/libomptarget/src/omptarget.cpp

  Log Message:
  -----------
  [OpenMP] Fix delete map type in ref count debug messages

For example, without this patch:

```
$ cat test.c
int main() {
  int x;
  #pragma omp target enter data map(alloc: x)
  #pragma omp target enter data map(alloc: x)
  #pragma omp target enter data map(alloc: x)
  #pragma omp target exit data map(delete: x)
  ;
  return 0;
}
$ clang -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda test.c
$ LIBOMPTARGET_DEBUG=1 ./a.out |& grep 'Creating\|Mapping exists\|last'
Libomptarget --> Creating new map entry with HstPtrBegin=0x00007ffddf1eaea8, TgtPtrBegin=0x00000000013bb040, Size=4, RefCount=1, Name=unknown
Libomptarget --> Mapping exists with HstPtrBegin=0x00007ffddf1eaea8, TgtPtrBegin=0x00000000013bb040, Size=4, RefCount=2 (incremented), Name=unknown
Libomptarget --> Mapping exists with HstPtrBegin=0x00007ffddf1eaea8, TgtPtrBegin=0x00000000013bb040, Size=4, RefCount=3 (incremented), Name=unknown
Libomptarget --> Mapping exists with HstPtrBegin=0x00007ffddf1eaea8, TgtPtrBegin=0x00000000013bb040, Size=4, RefCount=2 (decremented)
Libomptarget --> There are 4 bytes allocated at target address 0x00000000013bb040 - is not last
```

`RefCount` is reported as decremented to 2, but it ought to be reset
because of the `delete` map type, and `is not last` is incorrect.

This patch migrates the reset of reference counts from
`DeviceTy::deallocTgtPtr` to `DeviceTy::getTgtPtrBegin`, which then
correctly reports the reset.  Based on the `IsLast` result from
`DeviceTy::getTgtPtrBegin`, `targetDataEnd` then correctly reports `is
last` for any deletion.  `DeviceTy::deallocTgtPtr` is responsible only
for the final reference count decrement and mapping removal.

An obscure side effect of this patch is that a `delete` map type when
the reference count is infinite yields `DelEntry=IsLast=false` in
`targetDataEnd` and so no longer results in a
`DeviceTy::deallocTgtPtr` call.  Without this patch, that call is a
no-op anyway besides some unnecessary locking and mapping table
lookups.

Reviewed By: grokos

Differential Revision: https://reviews.llvm.org/D104560


Compare: https://github.com/llvm/llvm-project/compare/0c0628c92c0d...9fa5e3280d0b