cloud-hypervisor/docs/heap-profiling.md

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# Heap profiling
Cloud Hypervisor supports generating a profile using
[dhat](https://docs.rs/dhat/latest/dhat/) of the heap allocations made during
the runtime of the process.
## Building a suitable binary
This adds the symbol information to the release binary but does not otherwise
affect the performance.
```
$ cargo build --profile profiling --features "dhat-heap"
```
## Generating output
Cloud Hypervisor can then be run as usual. However it is necessary to run with `--seccomp false` as the profiling requires extra syscalls.
```
$ target/profiling/cloud-hypervisor \
--kernel ~/src/linux/vmlinux \
--pmem file=~/workloads/focal.raw \
--cpus boot=1 --memory size=1G \
--cmdline "root=/dev/pmem0p1 console=ttyS0" \
--serial tty --console off \
--api-socket /tmp/api1 \
--seccomp false
```
When the VMM exits a message like the following will be shown:
```
dhat: Total: 384,582 bytes in 3,512 blocks
dhat: At t-gmax: 133,885 bytes in 379 blocks
dhat: At t-end: 12,160 bytes in 20 blocks
dhat: The data has been saved to dhat-heap.json, and is viewable with dhat/dh_view.html
```
The JSON output can then be uploaded to [the dh_view tool](https://nnethercote.github.io/dh_view/dh_view.html) for analysis.