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# Profcollect
Profcollect is a system daemon that facilitates sampling profile collection and reporting for native
platform applications.
Profcollect can only be enabled on `userdebug` or `eng` builds.
## Supported Platforms
Currently Profcollect only supports collecting profiles from Coresight ETM enabled ARM devices.
Instructions to enable Coresight ETM can be found from the
[simpleperf manual](https://android.googlesource.com/platform/system/extras/+/refs/heads/master/simpleperf/doc/collect_etm_data_for_autofdo.md).
## Usage
Profcollect has two components: `profcollectd`, the system daemon, and `profcollectctl`, the command
line interface.
### Collection
`profcollectd` can be started from `adb` directly (under root), or automatically on system boot by
setting system property through:
```
adb shell device_config put profcollect_native_boot enabled true
```
Profcollect collects profiles periodically, as well as through triggers like app launch events. Only
a percentage of these events result in a profile collection to avoid using too much resource, these
are controlled by the following configurations:
| Event | Config |
|------------|------------------------|
| Periodic | collection\_interval |
| App launch | applaunch\_trace\_freq |
Setting the frequency value to `0` disables collection for the corresponding event.
### Processing
The raw tracing data needs to be combined with the original binary to create the AutoFDO branch
list. This is a costly process, thus it is done separately from the profile collection. Profcollect
attempts to process all the traces when the device is idle and connected to a power supply. It can
also be initiated by running:
```
adb shell profcollectctl process
```
### Reporting
#### Manual
After actively using the device for a period of time, the device should have gathered enough data to
generate a good quality PGO profile that represents typical system usage. Run the following command
to create a profile report:
```
$ adb shell profcollectctl report
Creating profile report
Report created at: 12345678-0000-abcd-8000-12345678abcd
```
You can then fetch the report by running (under root):
```
adb pull /data/misc/profcollectd/report/12345678-0000-abcd-8000-12345678abcd.zip
```
#### Automated Uploading to Server
*In development*
### Post Processing
For each trace file, run:
```
simpleperf inject \
-i {TRACE_FILE_NAME} \
-o {OUTPUT_FILE_NAME}.data \
--binary {BINARY_NAME} \
--symdir out/target/product/{PRODUCT_NAME}/symbols
```
Afterwards, run [AutoFDO](https://github.com/google/autofdo) to generate Clang PGO profiles:
```
create_llvm_prof \
--profiler text \
--binary=${BINARY_PATH} \
--profile=${INPUT_FILE_NAME} \
--out={OUTPUT_FILE_NAME}.profdata
```
Finally, merge all the PGO profiles into one profile:
```
find {INPUT_DIR} -name *.profdata > proflist
prebuilts/clang/host/linux-x86/llvm-binutils-stable/llvm-profdata merge \
--binary \
--sample \
--input-files proflist \
--output merged.profdata
```
More profile data usually generates better quality profiles. You may combine data from multiple
devices running the same build to improve profile quality, and/or reduce the performance impact for
each device (by reducing collection frequency).
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