Add runsc debug commands to Debugging section

content/docs/user_guide/debugging.md

@@ -31,3 +31,73 @@ sudo systemctl restart docker
 Run your container again, and inspect the files under `/tmp/runsc`. The log file
 with name `boot` will contain the strace logs from your application, which can
 be useful for identifying missing or broken system calls in gVisor.
+
+## Stack Trace
+
+`runsc debug --stacks` command allows stack traces to be collected while the 
+sandbox is running which can be useful to troubleshoot hangs or just to learn 
+more about gVisor. It connects to the sandbox process, collects a stack dump,
+and writes it to the console.
+
+Here is an example:
+
+```bash
+docker run --runtime=runsc --rm -d alpine sh -c "while true; do echo running; sleep .1; done"
+63254c6ab3a6989623fa1fb53616951eed31ac605a2637bb9ddba5d8d404b35b
+
+sudo runsc --root /var/run/docker/runtime-runsc/moby debug --stacks 63254c6ab3a6989623fa1fb53616951eed31ac605a2637bb9ddba5d8d404b35b
+```
+
+> Note: `--root` variable is provided by docker and is normally set to 
+> `/var/run/docker/runtime-[runtime-name]/moby`. If in doubt, `--root` is logged to
+> `runsc` logs.
+
+
+## Profiling
+
+`runsc` integrates with Go profiler and gives you easy commands to profile CPU
+and heap usage. First you need to enable `--profile` in the command line options
+before starting the container:
+
+```json
+{
+    "runtimes": {
+        "runsc-prof": {
+            "path": "/usr/local/bin/runsc",
+            "runtimeArgs": [
+                "--profile"
+            ]
+       }
+    }
+}
+```
+
+> Note: Enabling profiler loosens the seccomp protection added to the sandbox.
+
+Then restart docker to refresh the runtime options. While the container is running,
+execute `runsc debug` to collect profile information and save to a file. Here are
+the options available:
+
+ * **--profile-heap:** It generates heap profile to the speficied file.
+ * **--profile-cpu:** It enables CPU profiler, waits for `--profile-delay` seconds 
+   and generates CPU profile to the speficied file.
+
+Here is an example::
+
+```bash
+docker run --runtime=runsc-prof --rm -d alpine sleep 1000
+63254c6ab3a6989623fa1fb53616951eed31ac605a2637bb9ddba5d8d404b35b
+
+sudo runsc --root /var/run/docker/runtime-runsc-prof/moby debug --profile-heap=/tmp/heap.prof 63254c6ab3a6989623fa1fb53616951eed31ac605a2637bb9ddba5d8d404b35b
+sudo runsc --root /var/run/docker/runtime-runsc-prof/moby debug --profile-cpu=/tmp/cpu.prof --profile-delay=30 63254c6ab3a6989623fa1fb53616951eed31ac605a2637bb9ddba5d8d404b35b
+```
+
+The resulting files can be opened using `go tool pprof` or [pprof]
+(https://github.com/google/pprof/blob/master/doc/README.md). The examples below
+create image file (`.svg`) with the heap profile and writes the top functions
+using CPU to the console:
+
+```bash
+go tool pprof -svg /usr/local/bin/runsc /tmp/heap.prof
+go tool pprof -top /usr/local/bin/runsc /tmp/cpu.prof
+```