Add command for profiling and comparing toolchains #1028
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Couple nits really but this looks great, thanks! |
| anyhow::bail!("failed to annotate cachegrind output"); | ||
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| fs::write(path, output.stdout).context("failed to write `cg_annotate` output")?; |
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I also typically rustfilt the input to cg_annotate -- seems like a nice thing to add? I'm not sure it's necessary without symbol-mangling-version = v0, but I think that valgrind doesn't yet support that (at least not on all platforms).
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I have been using valgrind-3.17.0 which does have demangling support builtin based on libiberty (I think?). The only limitation is lack of support for symbols renamed during LTO, those with dot suffix, i.e., .llvm.*.
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Ubuntu 20.04 (latest LTS) only has 3.15, so I think we should try to avoid relying on the built-in demangling, I suspect it doesn't work. (Admittedly, I've been using a locally compiled version from git, so who knows...).
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Anyway, we can do this later if it becomes a problem for folks.
Current implementation allows using an arbitrary profiler, but the intended use case is profiling with cachegrind. When cachegrind is selected, the command will automatically compare results with `cg_diff` and post process output with `cg_annotate`.
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Note: it would be great for us to update the collector README with these changes so they're not so hidden. At some point, I think we should make a book on profiling and measuring perf of rustc (that can be linked to from the rustc-dev-guide). |
Current implementation allows using an arbitrary profiler, but the
intended use case is profiling with cachegrind. When cachegrind is
selected, the command will automatically compare results with
cg_diffand post process output with
cg_annotate.For example to compare two builds on ctfe-stress-4-doc benchmark: