gh-101282: Apply BOLT optimisations to libpython for shared builds - #104709
gh-101282: Apply BOLT optimisations to libpython for shared builds#104709erlend-aasland merged 4 commits into
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corona10
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Please update docs for BOLT_INSTRUMENT_FLAGS and BOLT_APPLY_FLAGS : https://docs.python.org/3.12/using/configure.html#performance-options
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corona10
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Overall LGTM.
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(This change is a quick and dirty way to merge some of the build system improvements I'm proposing in pythongh-101093 before the 3.12 feature freeze. I wanted to scope bloat myself to fix some longstanding deficiencies in the build system around profile-guided builds. But I'm getting soft resistance to the reviews so close to the freeze deadline and it is obvious that we need a simpler solution to hit the 3.12 deadline. While this change is quick and dirty, it attempts to not make things worse.) Before this change, we only applied bolt to the main python binary. After this change, we apply bolt to libpython if it is configured. In shared library builds, most of the C code is in libpython so it is critical to apply bolt to libpython to realize bolt benefits. This change also reworks how bolt instrumentation is applied. It effectively removes the readelf based logic added in pythongh-101525 and replaces it with a mechanism that saves a copy of the pre-bolt binary and restores that copy when necessary. This allows us to perform bolt optimizations without having to manually delete the output binary to force a new bolt run. We also add a new make target for purging bolt files and hook it up to `clean` so bolt state is purged when appropriate. `.gitignore` rules have been added to ignore files related to bolt. Before and after this refactor, `make` will no-op after a previous run. Both versions should also share common make DAG deficiencies where targets fail to trigger as often as they need to or can trigger prematurely in certain scenarios. e.g. after this change you may need to `rm profile-bolt-stamp` to force a bolt run because there aren't appropriate non-phony targets for bolt's make target to depend on. Fixing this is a non-trivial amount of work that will likely have to wait until the 3.13 window. To make it easier to iterate on custom BOLT settings, the flags to pass to instrumentation and application are now defined in configure and can be overridden by passing `BOLT_INSTRUMENT_FLAGS` and `BOLT_APPLY_FLAGS`.
Done in latest push. |
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erlend-aasland
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I cleaned up the docs and AC code; hope you don't mind.
I left some questions. Regarding BOLT technical stuff, I lean on Dong-hee's review.
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We appreciate if you don't force-push:
(This is also mentioned in the devguide.) |
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Thanks, Greg and Dong-hee! |
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(This change is a quick and dirty way to merge some of the build system improvements I'm proposing in gh-101093 before the 3.12 feature freeze. I wanted to scope bloat myself to fix some longstanding deficiencies in the build system around profile-guided builds. But I'm getting soft resistance to the reviews so close to the freeze deadline and it is obvious that we need a simpler solution to hit the 3.12 deadline. While this change is quick and dirty, it attempts to not make things worse.)
Before this change, we only applied bolt to the main python binary. After this change, we apply bolt to libpython if it is configured. In shared library builds, most of the C code is in libpython so it is critical to apply bolt to libpython to realize bolt benefits.
This change also reworks how bolt instrumentation is applied. It effectively removes the readelf based logic added in gh-101525 and replaces it with a mechanism that saves a copy of the pre-bolt binary and restores that copy when necessary. This allows us to perform bolt optimizations without having to manually delete the output binary to force a new bolt run.
We also add a new make target for purging bolt files and hook it up to clean so bolt state is purged when appropriate.
.gitignore rules have been added to ignore files related to bolt.
Before and after this refactor, make will no-op after a previous run. Both versions should also share common make DAG deficiencies where targets fail to trigger as often as they need to or can trigger prematurely in certain scenarios. e.g. after this change you may need to rm profile-bolt-stamp to force a bolt run because there aren't appropriate non-phony targets for bolt's make target to depend on. Fixing this is a non-trivial amount of work that will likely have to wait until the 3.13 window.
To make it easier to iterate on custom BOLT settings, the flags to pass to instrumentation and application are now defined in configure and can be overridden by passing BOLT_INSTRUMENT_FLAGS and BOLT_APPLY_FLAGS.