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CPU profiling

Learn to create and inspect a CPU profile.

CPU profiling

In non-HTTP programs the CPU profile is written to a file with runtime/pprof:

f, _ := os.Create("cpu.prof")
pprof.StartCPUProfile(f)
defer pprof.StopCPUProfile()

agirIs()

The profile takes about 100 samples per second, recording how often each function appears on the stack.

pprof commands

go tool pprof cpu.prof opens an interactive shell:

(pprof) top10        // the 10 most expensive functions
(pprof) list agirIs  // line-by-line cost
(pprof) web          // call graph

go tool pprof -http=:8081 cpu.prof opens a visual UI in the browser, including a flame graph.

Practice Profiled program

Write the CPU profile into a bytes.Buffer instead of a file with runtime/pprof: StartCPUProfile(&buf), sum 1 to 1,000,000 in a loop, StopCPUProfile(). Print the sum.

Starter code

main.go
package main

import (
    "bytes"
    "fmt"
    "runtime/pprof"
)

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import (
    "bytes"
    "fmt"
    "runtime/pprof"
)

func main() {
    var buf bytes.Buffer
    pprof.StartCPUProfile(&buf)
    toplam := 0
    for i := 1; i <= 1000000; i++ {
        toplam += i
    }
    pprof.StopCPUProfile()
    fmt.Println(toplam)
}

Expected output

500000500000

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 In <code>top</code> output, what is the difference between <code>flat</code> and <code>cum</code>?

  • cum is only the goroutine count
  • flat is the function's own time, cum includes what it calls Correct answer
  • flat is memory, cum is CPU
  • They are the same

Explanation: High flat means the function's own code is expensive; high cum with low flat means the cost is in the functions it calls.

2 Start the profile

Question 
f, _ := os.Create("cpu.prof")
pprof.____(f)
defer pprof.StopCPUProfile()
Answer 
f, _ := os.Create("cpu.prof")
pprof.StartCPUProfile(f)
defer pprof.StopCPUProfile()

Explanation: StartCPUProfile starts sampling; StopCPUProfile ends it and finalizes the file.

3 pprof command

Term Meaning
top Most expensive functions
list Line-by-line cost
web Call graph
-http Browser UI

All lessons in Advanced

1 Reflection

  1. The reflect package
  2. reflect.Type
  3. reflect.Value
  4. Reflecting struct fields
  5. Dynamic call
  6. Summary - Reflection

2 unsafe

  1. The unsafe package
  2. unsafe.Pointer
  3. Sizeof and Alignof
  4. Offsetof
  5. unsafe and slice
  6. Summary - unsafe

3 cgo

  1. What is cgo?
  2. Calling C code
  3. C data types
  4. Go-C conversion
  5. cgo and memory
  6. Summary - cgo

4 plugin

  1. The plugin package
  2. Building a plugin
  3. Loading a plugin
  4. Plugin symbol
  5. Plugin and error
  6. Summary - plugin

5 database/sql

  1. The database/sql package
  2. sql.Open
  3. Query and Exec
  4. Prepared statement
  5. Transaction
  6. Summary - database/sql

6 Middleware

  1. The middleware concept
  2. HTTP middleware
  3. Middleware chain
  4. Logging middleware
  5. Auth middleware
  6. Summary - Middleware

7 gRPC

  1. What is gRPC?
  2. Protobuf definition
  3. Compiling with protoc
  4. gRPC server
  5. gRPC client
  6. Summary - gRPC

8 Project: Microservice

  1. Service skeleton
  2. Database layer
  3. HTTP API
  4. Docker and deployment

9 Docker

  1. Dockerfile
  2. Multi-stage build
  3. scratch image
  4. docker-compose
  5. Build args and labels
  6. Summary - Docker

10 pprof

  1. What is pprof?
  2. CPU profiling
  3. Memory profiling
  4. go test -cpuprofile
  5. The trace tool
  6. Summary - pprof

11 Observability

  1. log/slog
  2. Metrics
  3. Tracing
  4. OpenTelemetry
  5. Health check
  6. Summary - Observability

12 Advanced final

  1. Challenge 1 - Reflection
  2. Challenge 2 - Microservice
  3. Challenge 3 - Performance
  4. Challenge 4 - Database