Profiling go programs

Question

I try to profile my go library, but I am stuck with the following output:

(pprof) top10
Total: 884 samples
     884 100.0% 100.0%      884 100.0% runtime.mach_semaphore_wait
       0   0.0% 100.0%      884 100.0% System

Which is not really helpful. My library reads a zip-file and parses the enclosed XML files (xlsx). When I move the profiling functions inside the lowest part of my library (where the actual xml decoding takes place), the output is not much 'better':

(pprof) top10   
Total: 884 samples
     884 100.0% 100.0%      884 100.0% fmt.(*fmt).formatFloat
       0   0.0% 100.0%      884 100.0% runtime.schedtrace

I know that this is a very vague question, but perhaps there are some helpful hints without having to provide the whole source code?

I have taken the profiler call from the golang blog entry and call the profiler with go tool pprof main profile after building main.go.

f, err := os.Create("profile")
if err != nil {
    log.Fatal(err)
}
pprof.StartCPUProfile(f)
defer pprof.StopCPUProfile()
    ... my source code here

Answer 1

It's a known bug that profiling doesn't work on Mac OS X. https://code.google.com/p/go/issues/detail?id=6047

The bug is in the Mac OS X kernel, and Russ Cox has a patch, described here: http://godoc.org/code.google.com/p/rsc/cmd/pprof_mac_fix , but that comes with dire warnings about screwing up your machine. In particular, there's known problems with the patch under Mavericks.