2022-10-19 11:35:55 +03:00
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bazel-zig-cc and llvm
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---------------------
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bazel-zig-cc has a performance issue when compiling many files. This repository
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reproduces that.
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Steps to reproduce
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------------------
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llvm14: 10-11 seconds to compile 96 binaries on an 8-core machine:
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```
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$ bazel clean; bazel shutdown; bazel build --extra_toolchains=@llvm_toolchain//:cc-toolchain-x86_64-linux ...
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INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.
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Starting local Bazel server and connecting to it...
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INFO: Analyzed 96 targets (41 packages loaded, 1458 targets configured).
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INFO: Found 96 targets...
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INFO: Elapsed time: 10.725s, Critical Path: 0.66s
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INFO: 481 processes: 289 internal, 192 linux-sandbox.
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INFO: Build completed successfully, 481 total actions
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```
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zig cc: 3.5 minutes. Anecdotally when looking at `htop` looks like it does not
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parallelize at all:
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```
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$ bazel clean; bazel shutdown; bazel build --platforms=@zig_sdk//libc_aware/platform:linux_amd64_gnu.2.28 ...
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INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.
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Starting local Bazel server and connecting to it...
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INFO: Analyzed 96 targets (41 packages loaded, 14394 targets configured).
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INFO: Found 96 targets...
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INFO: Elapsed time: 214.333s, Critical Path: 18.31s
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INFO: 385 processes: 193 internal, 192 linux-sandbox.
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INFO: Build completed successfully, 385 total actions
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```
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2022-10-26 00:00:18 +03:00
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Move sandbox to `/dev/shm` and reuse the sandboxes: 3 minutes and a bit.
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```
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$ bazel clean; bazel shutdown; bazel build --sandbox_base=/dev/shm --experimental_reuse_sandbox_directories --platforms=@zig_sdk//libc_aware/platform:linux_amd64_gnu.2.28 ...
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INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.
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Starting local Bazel server and connecting to it...
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INFO: Analyzed 96 targets (41 packages loaded, 14394 targets configured).
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INFO: Found 96 targets...
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INFO: Elapsed time: 194.643s, Critical Path: 25.35s
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INFO: 385 processes: 193 internal, 192 linux-sandbox.
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INFO: Build completed successfully, 385 total actions
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motiejus@motiejus-20NYS8QG0B:/code/test-zigcc$
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```
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