This patch updates the documentation with a summary of all necessary steps to be followed for performing afdo optimization

Signed-off-by: Andrea Brunato andrea.brunato@arm.com --- decoder/tests/auto-fdo/autofdo.md | 40 +++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+)

diff --git a/decoder/tests/auto-fdo/autofdo.md b/decoder/tests/auto-fdo/autofdo.md index 69ed152..b28b645 100644 --- a/decoder/tests/auto-fdo/autofdo.md +++ b/decoder/tests/auto-fdo/autofdo.md @@ -433,10 +433,50 @@ sudo ./set_strobing.sh 5000 10000 perf record -e cs_etm/@tmc_etr0/u --per-thread -- <your app>" perf inject -i perf.data -o inj.data --itrace=i100000il create_llvm_prof -binary=/path/to/binary -profile=inj.data -out=program.llvmprof +clang -O2 -fprofile-sample-use=program.llvmprof -o program program.c ```

Use `create_gcov` for gcc.

+## High Level Summary for recoding on Arm board and decoding on different host + +1. (on Arm board) + + sudo ./set_strobing.sh 5000 10000 + perf record -e cs_etm/@tmc_etr0/u --per-thread -- <your app>. + If you specify `-N, --no-buildid-cache`, perf will just take care of recording the target binary and nothing will be copied.<br> If you don't specify it, any recorded dynamic library will be copied to ~/.debug in the board. + +2. (on Arm board) `perf archive` which saves all the found libraries in a tar (internally, it looks into perf.data file and performs a lookup using perf-buildid-list --with-hits) +3. (on host) `scp` to copy perf.data and the .tar file generated from `perf archive`. +4. (on host) Run `tar xvf perf_data.tar.bz2 -C ~/.debug` to populate the buildid-cache +5. (on host) Double check the setup is correct: + + a. `perf buildid-list -i perf.data` gives you the list of dynamic libraries buildids whose trace has been recorded and saved in perf.data. + b. `perf buildid-cache --list` lists the dynamic libraries in the buildid cache that will be used by `perf inject`. + Make sure the output of (a) and (b) overlaps as in buildid value for those binaries you are interested into optimizing with afdo. + +6. (on host) `perf inject -i perf.data -o inj.data --itrace=i100000il` will check for the dynamic libraries using the buildid inside the buildid-cache and post-process the trace.<br> buildids have to be the same, otherwise it won't be possible to post-process the trace. + +7. (on host) `create_llvm_prof -binary=/path/to/binary -profile=inj.data -out=program.llvmprof` takes the output from perf-inject and tranforms it into a format that the compiler can read. +8. (on host) `clang -O2 -fprofile-sample-use=program.llvmprof -o program program.c` to make clang use the produced profile.<br> + If you are confident enough that your profile is accurate, you can add the `-fprofile-sample-accurate` flag, which will penalize all the callsites without corresponding profile, marking them as cold. + +If you are using the same host for both building the binary to be traced and re-building it with afdo: + +1. You won't need to copy back any dynamic libraries from the board (since you already have them), and can use `--no-buildid-cache` when recording +2. You have to make sure the relevant dynamic libraries to be optimized are present in the buildid-cache. + +You can easily add a dynamic library manually into the build-id cache by running: + +`perf buildid-cache --add <path/to/library/or/binary> -vvv` + +You can easily check what is currently contained in you buildid-cache by running: + +`perf buildid-cache --list` + +You can check the buildid of a given binary/dynamic library: + +`file <path/to/dynamic/library>`

## References