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65 lines
1.9 KiB
Markdown
65 lines
1.9 KiB
Markdown
# Profiling
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`perf` can be used to profile the `cloud-hypervisor` binary but it is necessary to make some modifications to the build in order to produce a binary that gives useful results.
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## Building a suitable binary
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Modify the `Cargo.toml` file to add `debug = 1` to the `[profile.release]` block. It should look like this:
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```
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[profile.release]
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lto = true
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debug = 1
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```
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This adds the symbol information to the release binary but does not otherwise affect the performance.
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The binary must also be built with frame pointers included so that the call graph can be captured by the profiler.
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```
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$ cargo clean && RUSTFLAGS='-C force-frame-pointers=y' cargo build --release
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```
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## Profiling
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`perf` may then be used in the usual manner:
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e.g.
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```
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$ perf record -g target/release/cloud-hypervisor \
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--kernel ~/src/linux/vmlinux \
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--pmem file=~/workloads/focal.raw \
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--cpus boot=1 --memory size=1G \
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--cmdline "root=/dev/pmem0p1 console=ttyS0" \
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--serial tty --console off \
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--api-socket=/tmp/api1
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```
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For analysing the samples:
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```
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$ perf report -g
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```
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If profiling with a network device attached either the TAP device must be already created and configured or the profiling must be done as root so that the TAP device can be created.
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## Userspace only profiling with LBR
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The use of LBR (Last Branch Record; available since Haswell) offers lower
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overhead if only userspace profiling is required. This lower overhead can allow
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a higher frequency of sampling. This also removes the requirement to compile
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with custom `RUSTFLAGS` however debug symbols should still be included:
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e.g.
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```
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$ perf record --call-graph lbr --all-user --user-callchains -g target/release/cloud-hypervisor \
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--kernel ~/src/linux/vmlinux \
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--pmem file=~/workloads/focal.raw \
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--cpus boot=1 --memory size=1G \
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--cmdline "root=/dev/pmem0p1 console=ttyS0" \
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--serial tty --console off \
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--api-socket=/tmp/api1
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```
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