[Docs][llvm-exegesis] Clarify AArch64 support #114989
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sjoerdmeijer
requested review from
boomanaiden154,
davemgreen,
john-brawn-arm,
kpdev and
legrosbuffle
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|
@llvm/pr-subscribers-llvm-binary-utilities @llvm/pr-subscribers-tools-llvm-exegesis Author: Sjoerd Meijer (sjoerdmeijer) ChangesClaiming AArch64 support for llvm-exegesis is a bit of a stretch in my opinion as only a couple of opcodes with GPR64 operands will work, so I propose to clarify that AArch64 support is very experimental. Also added some clarifications about its libpfm4 dependency. Full diff: https://github.com/llvm/llvm-project/pull/114989.diff 2 Files Affected:
diff --git a/llvm/docs/CommandGuide/llvm-exegesis.rst b/llvm/docs/CommandGuide/llvm-exegesis.rst
index fdf17c7fe41285..102c4eb47e9d60 100644
--- a/llvm/docs/CommandGuide/llvm-exegesis.rst
+++ b/llvm/docs/CommandGuide/llvm-exegesis.rst
@@ -33,11 +33,13 @@ snippets.
SUPPORTED PLATFORMS
-------------------
-:program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM (AArch64
-only), MIPS, and PowerPC (PowerPC64LE only) on Linux for benchmarking. Not all
-benchmarking functionality is guaranteed to work on every platform.
-:program:`llvm-exegesis` also has a separate analysis mode that is supported
-on every platform that LLVM is.
+:program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM
+(AArch64 only and very experimental), MIPS, and PowerPC (PowerPC64LE only) on
+Linux for benchmarking. Not all benchmarking functionality is guaranteed to
+work on every platform. :program:`llvm-exegesis` also has a separate analysis
+mode that is supported on every platform that LLVM is. See README.md for
+more information on the libpfm4 dependency and how to configure and build
+:program:`llvm-exegesis` from source.
SNIPPET ANNOTATIONS
-------------------
diff --git a/llvm/tools/llvm-exegesis/README.md b/llvm/tools/llvm-exegesis/README.md
index f606fbf8e0eb64..f68a42b05064b4 100644
--- a/llvm/tools/llvm-exegesis/README.md
+++ b/llvm/tools/llvm-exegesis/README.md
@@ -13,8 +13,16 @@ Analysis mode in `llvm-exegesis` is supported on all platforms on which LLVM is.
#### Currently Supported Operating Systems for Benchmarking
Currently, `llvm-exegesis` only supports benchmarking on Linux. This is mainly
-due to a dependency on the Linux perf subsystem for reading performance
-counters.
+due to a dependency on the Linux perf subsystem and libpfm4 for reading
+performance counters. For benchmarking, LLVM needs to be configured and build
+with `LLVM_ENABLE_LIBPFM` enabled. Benchmarking might fail if the target cpu is
+not supported by libpfm. This can be checked by putting libpfm in verbose/debug
+mode with environment variables `LIBPFM_VERBOSE` and `LIBFM_DEBUG`. If libpfm
+is installed in a non-standard location, LLVM can be configured to look for the
+libpfm library and header file locations by setting environment variables
+`LIBRARY_PATH`, `C_INCLUDE_PATH`, and `CPLUS_INCLUDE_PATH`. In that case variable
+`LD_LIBRARY_PATH` needs to be set too so that `llvm-exegesis` can find the
+library at execution time.
The subprocess execution mode and memory annotations currently only supports
Linux due to a heavy reliance on many Linux specific syscalls/syscall
@@ -28,7 +36,7 @@ architectures:
* 64-bit only due to this being the only implemented calling convention
in `llvm-exegesis` currently.
* ARM
- * AArch64 only
+ * Very experimental AArch64 support only, most opcodes probably won't work.
* MIPS
* PowerPC (PowerPC64LE only)
|
boomanaiden154
requested changes
Nov 5, 2024
| :program:`llvm-exegesis` also has a separate analysis mode that is supported | ||
| on every platform that LLVM is. | ||
| :program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM | ||
| (AArch64 only and very experimental), MIPS, and PowerPC (PowerPC64LE only) on |
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I would explicitly state here that snippet generation is experimental. In process snippet execution should "just work".
Maybe something like "AArch64 only, snippet generation support is sparse".
llvm/tools/llvm-exegesis/README.md
Outdated
| in `llvm-exegesis` currently. | ||
| * ARM | ||
| * AArch64 only | ||
| * Very experimental AArch64 support only, most opcodes probably won't work. |
Contributor
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Same clarification here.
llvm/tools/llvm-exegesis/README.md
Outdated
| Currently, `llvm-exegesis` only supports benchmarking on Linux. This is mainly | ||
| due to a dependency on the Linux perf subsystem for reading performance | ||
| counters. | ||
| due to a dependency on the Linux perf subsystem and libpfm4 for reading |
Contributor
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This should probably go in the LLVM CMake documentation. This page isn't intended to provide detailed build directions, and people are more likely to look there.
| (AArch64 only and very experimental), MIPS, and PowerPC (PowerPC64LE only) on | ||
| Linux for benchmarking. Not all benchmarking functionality is guaranteed to | ||
| work on every platform. :program:`llvm-exegesis` also has a separate analysis | ||
| mode that is supported on every platform that LLVM is. See README.md for |
Contributor
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Reference the CMake documentation here. It's a bit odd to reference a README from proper documentation.
Claiming AArch64 support for llvm-exegesis is a bit of a stretch, so clarify that that its support is very experimental. Also added some clarifications about its libpfm4 dependency.
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Thanks for the review! I have addressed all comments, I think. |
davemgreen
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Nov 7, 2024
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This matches my understanding of the support level in AArch64 at the moment. Thanks
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Claiming AArch64 support for llvm-exegesis is a bit of a stretch in my opinion as only a couple of opcodes with GPR64 operands will work, so I propose to clarify that AArch64 support is very experimental. Also added some clarifications about its libpfm4 dependency.