Online manpages like https://linux.die.net/man/1/perf-record suggest that there is an option for Linux perf command that supports incremental profiling, i.e. merging the profiling data from multiple different runs, via perf record --append. However, on my system with perf version 4.15.18, the option is missing. Is my perf version too new, or too old, to use the --append option? Alternatively, if the --append option is missing, is there another way for me to merge/append perf results from multiple runs and do incremental profiling?
This question arose when doing sampling-based profiling using LLVM. In LLVM, instrumentation-based profiling supports merging profile data across multiple runs, and I was wondering if we can do the same thing with perf.
It was removed quite a while ago, see https://lore.kernel.org/patchwork/patch/391730/ and related discussion here: https://marc.info/?l=linux-kernel&m=137031146932578&w=2. Looks like the way --append is implemented is rather simple: simply by changing the write mode of profiling data to "append", and it doesn't work well with perf report, so they decided to remove it.
There seems to be the option --timestamp-filename of timestamping the output filename, which is potentially useful to batch-sample programs using perf. When doing sampling-based optimization in LLVM, we can then use AutoFDO to convert the profiles into LLVM-readable profiles and use llvm-profdata merge to merge everything.