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Clarify documentation around profiling based on user feedback #23858

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bradcray opened this issue Nov 15, 2023 · 1 comment · Fixed by #23861
Closed

Clarify documentation around profiling based on user feedback #23858

bradcray opened this issue Nov 15, 2023 · 1 comment · Fixed by #23861
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area: Docs type: Refactor user issue

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@bradcray
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bradcray commented Nov 15, 2023 •
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This user interaction in gitter suggests that our profiling documentation isn't particularly up-to-date w.r.t. the LLVM back-end coming online, and checking a few key documents, it looks like other clarifications are possible as well (like that building with PROFILE=1 or similar options only affects the runtime and third-party code, not the Chapel installation as a whole).
@psath
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psath commented Nov 15, 2023

The settings I was able to get gprof working on both 1.31 and 1.32 were as follows:
Runtime/compiler built with:

CHPL_GPU=cpu
CHPL_LOCALE_MODEL=flat
CHPL_HOST_COMPILER=gnu
CHPL_TARGET_COMPILER=gnu
DEBUG=0
OPTIMIZE=1
PROFILE=1

User code built with:

--fast --ccflags -pg --ldflags -pg

(GPU loops were manually refactored to run on CPU to steer clear of #23859)

This was referenced Nov 15, 2023
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bradcray added a commit that referenced this issue Nov 16, 2023
@bradcray
Cleanups to docs and compiler w.r.t. -pg and particularly the LLVM …
b92fffc 
…back-end (#23861)

[reviewed by @jabraham17]

Based on user interactions this week, this refreshes some documentation
w.r.t. profiling and also adds a warning to the compiler if trying to
use the `-pg` flag with the LLVM back-end to indicate that it is not
supported. Specifically it:

* adds a warning to the compiler when the target compiler is LLVM and
ccflags or ldflags contains the string `-pg`
* adds a test for this warning
* adds a caveat to the documentation about profiling generated code
using `gprof` not being supported by the LLVM back-end
* adds an indication that other performance analysis tools may be used
with Chapel without providing instructions
* refreshes the profiling-related text now that this developer-oriented
document is available on the web docs and readily findable by searching.
Specifically, it:
  * fixed grammatical errors (hopefully without introducing new ones)
  * tries to linearize and tighten up the descriptions
* removes a bunch of stuff that feels very advanced developer-oriented
and potentially outdated
* clarifies that settings made at `make` time only affect the compiler,
runtime, and third-parties, not the compiler's behavior
* re-alphabetizes the table of major build options available in the
Makefiles

Resolves #23858
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Cleanups to docs and compiler w.r.t. -pg and particularly the LLVM back-end bradcray/chapel
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@psath @bradcray