doc: include poor-performance diagnostic (#4928)

Author: RafaelGSS

locale/en/docs/guides/diagnostics/index.md

@@ -17,5 +17,6 @@ This is the available set of diagnostics guides:
 
 * [Memory](/en/docs/guides/diagnostics/memory)
 * [Live Debugging](/en/docs/guides/diagnostics/live-debugging)
+* [Poor Performance](/en/docs/guides/diagnostics/poor-performance)
 
 [Diagnostics Working Group]: https://github.com/nodejs/diagnostics

locale/en/docs/guides/diagnostics/poor-performance/index.md

@@ -0,0 +1,36 @@
+---
+title: Poor Performance - Diagnostics
+layout: docs.hbs
+---
+
+# Poor Performance
+
+In this document you can learn about how to profile a Node.js process.
+
+* [Poor Performance](#poor-performance)
+  * [My application has a poor performance](#my-application-has-a-poor-performance)
+    * [Symptoms](#symptoms)
+    * [Debugging](#debugging)
+
+## My application has a poor performance
+
+### Symptoms
+
+My applications latency is high and I have already confirmed that the bottleneck
+is not my dependencies like databases and downstream services. So I suspect that
+my application spends significant time to run code or process information.
+
+You are satisfied with your application performance in general but would like to
+understand which part of our application can be improved to run faster or more
+efficient. It can be useful when we want to improve the user experience or save
+computation cost.
+
+### Debugging
+
+In this use-case, we are interested in code pieces that use more CPU cycles than
+the others. When we do this locally, we usually try to optimize our code.
+
+This document provides two simple ways to profile a Node.js application:
+
+* [Using V8 Sampling Profiler](https://nodejs.org/en/docs/guides/simple-profiling/)
+* [Using Linux Perf](/en/docs/guides/diagnostics/poor-performance/using-linux-perf)

locale/en/docs/guides/diagnostics/poor-performance/using-linux-perf.md

@@ -0,0 +1,87 @@
+---
+title: Poor Performance - Using Linux Perf
+layout: docs.hbs
+---
+
+# Using Linux Perf
+
+[Linux Perf](https://perf.wiki.kernel.org/index.php/Main_Page) provides low level CPU profiling with JavaScript,
+native and OS level frames.
+
+**Important**: this tutorial is only available on Linux.
+
+## How To
+
+Linux Perf is usually available through the `linux-tools-common` package. Through either `--perf-basic-prof` or
+`--perf-basic-prof-only-functions` we are able to start a Node.js application supporting _perf_events_.
+
+`--perf-basic-prof` will always write to a file (/tmp/perf-PID.map), which can lead to infinite disk growth.
+If that’s a concern either use the module: [linux-perf](https://www.npmjs.com/package/linux-perf)
+or `--perf-basic-prof-only-functions`.
+
+The main difference between both is that `--perf-basic-prof-only-functions` produces less output, it is a viable option
+for production profiling.
+
+```console
+# Launch the application an get the PID
+$ node --perf-basic-prof-only-functions index.js &
+[1] 3870
+```
+
+Then record events based in the desired frequency:
+
+```console
+$ sudo perf record -F 99 -p 3870 -g
+```
+
+In this phase, you may want to use a load test in the application in order to generate more records for a reliable
+analysis. When the job is done, close the perf process by sending a SIGINT (Ctrl-C) to the command.
+
+The `perf` will generate a file inside the `/tmp` folder, usually called `/tmp/perf-PID.map`
+(in above example: `/tmp/perf-3870.map`) containing the traces for each function called.
+
+To aggregate those results in a specific file execute:
+
+```console
+$ sudo perf script > perfs.out
+```
+
+```console
+$ cat ./perfs.out
+node 3870 25147.878454:          1 cycles:
+        ffffffffb5878b06 native_write_msr+0x6 ([kernel.kallsyms])
+        ffffffffb580d9d5 intel_tfa_pmu_enable_all+0x35 ([kernel.kallsyms])
+        ffffffffb5807ac8 x86_pmu_enable+0x118 ([kernel.kallsyms])
+        ffffffffb5a0a93d perf_pmu_enable.part.0+0xd ([kernel.kallsyms])
+        ffffffffb5a10c06 __perf_event_task_sched_in+0x186 ([kernel.kallsyms])
+        ffffffffb58d3e1d finish_task_switch+0xfd ([kernel.kallsyms])
+        ffffffffb62d46fb __sched_text_start+0x2eb ([kernel.kallsyms])
+        ffffffffb62d4b92 schedule+0x42 ([kernel.kallsyms])
+        ffffffffb62d87a9 schedule_hrtimeout_range_clock+0xf9 ([kernel.kallsyms])
+        ffffffffb62d87d3 schedule_hrtimeout_range+0x13 ([kernel.kallsyms])
+        ffffffffb5b35980 ep_poll+0x400 ([kernel.kallsyms])
+        ffffffffb5b35a88 do_epoll_wait+0xb8 ([kernel.kallsyms])
+        ffffffffb5b35abe __x64_sys_epoll_wait+0x1e ([kernel.kallsyms])
+        ffffffffb58044c7 do_syscall_64+0x57 ([kernel.kallsyms])
+        ffffffffb640008c entry_SYSCALL_64_after_hwframe+0x44 ([kernel.kallsyms])
+....
+```
+
+The raw output can be a bit hard to understand so typically the raw file is used to generate flamegraphs for a better
+visualization.
+
+![Example nodejs flamegraph](https://user-images.githubusercontent.com/26234614/129488674-8fc80fd5-549e-4a80-8ce2-2ba6be20f8e8.png)
+
+To generate a flamegraph from this result, follow [this tutorial](https://nodejs.org/en/docs/guides/diagnostics-flamegraph/#create-a-flame-graph-with-system-perf-tools)
+from step 6.
+
+Because `perf` output is not a Node.js specific tool, it might have issues with how JavaScript code is optimized in
+Node.js. See [perf output issues](https://nodejs.org/en/docs/guides/diagnostics-flamegraph/#perf-output-issues) for a
+futher reference.
+
+## Useful Links
+
+* https://nodejs.org/en/docs/guides/diagnostics-flamegraph/
+* https://www.brendangregg.com/blog/2014-09-17/node-flame-graphs-on-linux.html
+* https://perf.wiki.kernel.org/index.php/Main_Page
+* https://blog.rafaelgss.com.br/node-cpu-profiler