fixes an issue with macro directives for !$acc kernels

[sbryngelson]

User description

The #883 created an issue that substituted !$acc parallel for !$acc kernels in all of 3 whole places (!!). It turns out this does not work on NVHPC. This is a stopgap fix. @prathi-wind will fix it up more properly.

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PR Type

Bug fix

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Description

• Replace GPU_PARALLEL macro with !$acc kernels directives

• Fix NVHPC compiler compatibility issues

• Update OpenACC directives in data output and time stepping modules

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Changes diagram

flowchart LR
  A["GPU_PARALLEL macro"] -- "replace with" --> B["!$acc kernels directives"]
  B --> C["NVHPC compatibility"]

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Changes walkthrough 📝

Relevant files

Bug fix

m_data_output.fpp Update OpenACC directives in data output module                    src/simulation/m_data_output.fpp Replace #:call GPU_PARALLEL() with !$acc kernels for icfl_max_loc calculation Update viscous flow section with !$acc kernels directives for vcfl_max_loc and Rc_min_loc +7/-7      m_time_steppers.fpp Fix OpenACC directives in time stepping module                      src/simulation/m_time_steppers.fpp Replace #:call GPU_PARALLEL() with !$acc kernels for dt_local calculation +3/-3

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[qodo-code-review]

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Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 No relevant tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Duplicate Code The same pattern of wrapping maxval/minval operations with !$acc kernels directives is repeated multiple times. This could be refactored into a reusable macro or subroutine to reduce code duplication and improve maintainability. !$acc kernels icfl_max_loc = maxval(icfl_sf) !$acc end kernels if (viscous) then !$acc kernels vcfl_max_loc = maxval(vcfl_sf) Rc_min_loc = minval(Rc_sf) !$acc end kernels end if Performance Concern Using !$acc kernels for a single minval operation may not provide optimal GPU performance compared to !$acc parallel. The kernels directive relies on compiler analysis which may not be as efficient for simple reduction operations. !$acc kernels dt_local = minval(max_dt) !$acc end kernels

[Copilot]

Pull Request Overview

This PR replaces the custom GPU_PARALLEL() macro with raw OpenACC kernels directives as a stopgap for NVHPC compatibility.

• Substituted #:call GPU_PARALLEL()/#:endcall GPU_PARALLEL with !$acc kernels/!$acc end kernels
• Applied the change in both the time-stepping and data-output modules

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/simulation/m_time_steppers.fpp	Replaced GPU_PARALLEL macro around minval(max_dt) with kernels
src/simulation/m_data_output.fpp	Replaced GPU_PARALLEL macro around maxval/minval calls

Comments suppressed due to low confidence (3)

src/simulation/m_time_steppers.fpp:996

• Wrapping a scalar minval call in a kernels region may incur unnecessary kernel launch overhead and may not generate a reduction on the device. Consider using !$acc parallel loop reduction(min:dt_local) around the explicit loop over max_dt with a collapse if multiple dimensions are involved.

        !$acc kernels

src/simulation/m_data_output.fpp:319

• Enclosing maxval(icfl_sf) in a kernels region may not produce an efficient reduction; consider converting this to a !$acc parallel loop reduction(max:icfl_max_loc) over the underlying array to leverage device-side reductions.

        !$acc kernels

src/simulation/m_data_output.fpp:323

• This kernels region wraps two scalar reductions (vcfl_max_loc, Rc_min_loc); you may get better performance by using a combined !$acc parallel loop reduction(max:vcfl_max_loc) reduction(min:Rc_min_loc) over the loop indices instead of kernels.

            !$acc kernels

[qodo-code-review]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
General	Separate reduction operations into individual kernels Consider using separate kernel regions for each reduction operation. Multiple reductions in a single kernel may not be optimal for GPU performance and could lead to synchronization issues. src/simulation/m_data_output.fpp [323-326] !$acc kernels vcfl_max_loc = maxval(vcfl_sf) +!$acc end kernels +!$acc kernels Rc_min_loc = minval(Rc_sf) !$acc end kernels Suggestion importance[1-10]: 5 __ Why: This is a valid performance consideration, as splitting multiple reduction operations into separate kernels can sometimes improve GPU performance, although the benefit is not guaranteed and depends on the compiler and hardware.	Low
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[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 43.71%. Comparing base (0900648) to head (534a8a9).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/simulation/m_data_output.fpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #926      +/-   ##
==========================================
+ Coverage   43.68%   43.71%   +0.02%     
==========================================
  Files          68       68              
  Lines       18363    18360       -3     
  Branches     2295     2292       -3     
==========================================
+ Hits         8022     8026       +4     
+ Misses       8949     8945       -4     
+ Partials     1392     1389       -3     

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