怎么才能看到系统进程的trace呢？

使用命令：`java -jar rhea-trace-shell.jar -a com.my.app -t 10 -o output.pb rhea.all -r sched -fullClassName -mode simple`抓取trace后，打开output.pb，没有系统的trace信息，比如system_server进程信息，使用systrace是有的。
在btrace2上该怎么查看呢？

Start by reproducing the exact java command and opening output.pb, then compare its process information with the corresponding systrace result. Investigate how btrace2 handles system processes such as system_server; the issue is resolved when the supported way to capture and view that information is confirmed or the limitation is documented.

Written by the indexing model from the issue text.