| # Dart support for perf |
| |
| ## Pause `perf stat` recording while GC is running (or vice versa) |
| |
| `perf stat` supports starting and stopping the recording via `--control` and the |
| Dart VM can be instructed to either stop the recording while GC is running, or |
| specifically start while GC is running (and stop when GC is finished) with |
| `--perf_ctl_fd`, `--perf_ctl_fd_ack` (for file handles) and `--perf_ctl_usage` |
| (1 or 2) to specify if it should be paused while GCing (1) or started (and |
| stoped) while GCing (2). |
| |
| These options can for instance be useful for testing performance changes in AOT |
| compiled dart together with `--deterministic`. |
| |
| As an example one could run a script like this: |
| |
| ``` |
| DART=$1 |
| shift |
| AOTSNAPSHOT=$1 |
| shift |
| |
| [...] |
| |
| perf_ctl_fd=$ctl_fd perf_ctl_fd_ack=$ctl_fd_ack perf stat --delay=-1 --control fd:${ctl_fd},${ctl_fd_ack} -B -e "task-clock:u,context-switches:u,cpu-migrations:u,page-faults:u,cycles:u,instructions:u,branch-misses:u" $DART --perf_ctl_fd=${ctl_fd} --perf_ctl_fd_ack=${ctl_fd_ack} --perf_ctl_usage=1 --deterministic $AOTSNAPSHOT $@ |
| |
| [...] |
| ``` |
| |
| (the missing pieces can be found in the perf stat man page). |
| |
| This will start `perf stat` paused (which would require the run dart |
| aot-compiled script to start it when it wants to) and where the VM pauses `perf` |
| while doing GC. Note that the recording will be started when GC is done, even if |
| it wasn't started before. |
