Go Profiling

Just a collection of tools and commands to help profile and find areas to improve on in your Go code.

Test profiling

• go test -race
  • Runs the tests with the race detector activated.
• go test -benchmem
  • Prints allocation statistics during benchmarks(number of bytes, and number of allocations).
• go test -blockprofile out
  • Writes a profile to out containing goroutine blocking statistics for use with go tool pprof.
• go test -cpuprofile out
  • Writes a profile to out containing CPU statistics for use with go tool pprof.
• go test -memprofile out
  • Writes a profile to out containing memory statistics for use with go tool pprof.
• go test -mutexprofile out
  • Writes a profile to out containing mutex contention statistics for use with go tool pprof.
• go test -trace out
  • Writes a profile to out containing the execution trace of the tests for use with go tool pprof.
• go test -coverprofile out
  • Writes a code coverage profile to out for use with go tool cover -html.

Creating runtime profiling stats

• GODEBUG="allocfreetrace=1,gctrace=1,scheddetail=1,schedtrace=X"
  • Setting $GODEBUG makes the runtime print extra debugging information that can be useful for figuring out what's going on in at any moment.
  • allocfreetrace=1 Prints every allocation and free including the related stack trace to stderr(this is a lot to print, so it'll be a good idea to redirect stderr to a file).
  • gctrace=1 Prints every GC cycle and stats about the cycle(for more info read here).
  • scheddetail=1,schedtrace=X Every X milliseconds prints detailed information about the runtime(including goroutines, OS threads, and "processors"). For a quick overview, set scheddetail=0.
• go build -race -gcflags "-m"
  • -race builds the binary with the race detector activated.
  • -gcflags "-m" builds the binary with debug printing various information about optimizations as well as heap escapes and leaking params.
• net/http/pprof
  • Attaches a few routes under the /debug/pprof/ endpoint that provide a profile that can be used with go tool pprof.
• net/http/httptrace
  • Allows you to trace http requests to determine connection reuse and dns lookup optimizations.

Reading and visualizing runtime profiling stats

• go tool pprof
  • Runs the pprof cli for the given profile http endpoint or profile file, including the binary also includes specifics about each function.
• go tool pprof -inuse_space
  • Runs the same as the above except the profile must be a memory profile, and profiles the amount of memory in use.
• go tool pprof -inuse_objects
  • Runs the same as the above except the profile must be a memory profile, and profiles the number of objects used in memory.
• go tool pprof -alloc_space
  • Runs the same as the above except the profile must be a memory profile, and profiles the amount of memory allocated.
• go tool pprof -alloc_objects
  • Runs the same as the above except the profile must be a memory profile, and profiles the number of objects allocated.
• go tool pprof -total_delay
  • Runs the same as the above except the profile must be a blocking or mutex contention profile, and profiles the delay of contention points(blocking goroutines, mutex contention).
• go tool pprof -contentions
  • Runs the same as the above except the profile must be a blocking or mutex contention profile, and profiles the points of contention(blocking goroutines, mutex contention).
• go tool trace
  • Opens a browser window with links to various execution information gathered from the profile.
  • View trace displays a visual representation of the programs lifetime.
  • Goroutine analysis contains every goroutine and the time spent scheduling, in GC, networking, and code execution.
  • Network blocking profile provides timing for every level of the network stack to see where blocking is occurring.
  • Synchronization blocking profile provdes timing for every level of the stack showing where time is spent blocked during synchronization.
  • Syscall blocking profile provides timing for syscalls to show where time is most spent in the kernel.
  • Scheduler latency profile provides timing for scheduler level information showing where time is most spent scheduling.
• github.com/davecheney/gcvis
  • Provides a visual representation of memory usage and the GC in real time.
• github.com/google/gops
  • Provides access to print runtime information from Go processes by PIDs.
• github.com/derekparker/delve
  • Delve is a debugger providing a command line access as well as editor integrations.

Benchmarking tools

• https://github.com/codesenberg/bombardier
  • Is a HTTP benchmarking tool providing latency statistics, throughput, etc.
• golang.org/x/tools/cmd/benchcmp
  • Compares the output of two benchmarks from go test and displays the deltas between the two.