LBR vs DWARF vs fp 的性能记录选择有什么作用？

Question

When I use the perf record on my code, I find three choices for the --call-graph option: lbr (last branch record), dwarf and fp .

What is difference between these?

Answer 1

The option --call-graph refers to the collection of call graphs / call chains, ie the function stack for a sample.

The default, fp , uses frame pointers . This is very efficient but can be unreliable, particularly for optimized code. By explicitly using -fno-omit-frame-pointer , you can ensure that this is available for your code. Nevertheless, the result for libraries may vary.

With dwarf , perf actually collects and stores a part of the stack memory itself and unwinds it with post-processing. This can be very resource consuming and may have limited stack depth. The default stack memory chunk is 8 kiB, but can be configured.

lbr stands for last branch records . This is a hardware mechanism support by Intel CPUs. This will probably offer the best performance at the cost of portability. lbr is also limited to userspace functions.