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Recommend perf for higher sampling frequency

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Felix Geisendörfer
2021-09-12 13:40:49 +02:00
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@ -219,7 +219,7 @@ If you see system calls such as `syscall.Read()` or `syscall.Write()` using a lo
There are a few known issues and limitations of the CPU profiler that you might want to be aware of:
- 🐞 A known issue on linux is that the CPU profiler struggles to achieve a sample rate beyond `250Hz`. This is usually not a problem, but can lead to bias if your CPU utilization is very spiky. For more information on this, check out this [GitHub issue](https://github.com/golang/go/issues/35057).
- 🐞 A known issue on linux is that the CPU profiler struggles to achieve a sample rate beyond `250Hz`. This is usually not a problem, but can lead to bias if your CPU utilization is very spiky. For more information on this, check out this [GitHub issue](https://github.com/golang/go/issues/35057). Meanwhile you can use Linux perf which supports higher sampling frequencies.
- ⚠️️ You can call [`runtime.SetCPUProfileRate()`](https://pkg.go.dev/runtime#SetCPUProfileRate) to adjust the CPU profiler rate before calling `runtime.StartCPUProfile()`. This will print a warning saying `runtime: cannot set cpu profile rate until previous profile has finished`. However, it still works within the limitation of the bug mentioned above. This issue was [initially raised here](https://github.com/golang/go/issues/40094), and there is an [accepted proposal for improving the API](https://github.com/golang/go/issues/42502).
- ⚠️ The maximum number of nested function calls that can be captured in stack traces by the CPU profiler is currently [`64`](https://sourcegraph.com/search?q=context:global+repo:github.com/golang/go+file:src/*+maxCPUProfStack+%3D&patternType=literal). If your program is using a lot of recursion or other patterns that lead to deep stack depths, your CPU profile will include stack traces that are truncated. This means you will miss parts of the call chain that led to the function that was active at the time the sample was taken.