Add information about tweaking iogpu.wired_limit_mb (NVIDIA#308)

Signed-off-by: Maciej Szulik <maszulik@redhat.com>

lab-troubleshoot.md

@@ -2,7 +2,29 @@
 
 This document is for commonly found problems and their solutions when using `lab`.
 
-## `gh` Troubleshooting
+## `lab` troubleshooting
+
+### Long `lab generate` on MacOS issue
+If you notice `lab generate` being very slow for you, several hours or more.
+Check [this discussion](https://github.com/ggerganov/llama.cpp/discussions/2182#discussioncomment-7698315)
+which is suggesting to tweak the GPU limit, which MacOS assigns. By default it's
+around 60%-70% of your total RAM available, which is expressed as 0:
+```
+$ sudo sysctl iogpu.wired_limit_mb
+iogpu.wired_limit_mb = 0
+```
+You can set it to any number, although it's advisable to leave 4-6GB for MacOS.
+
+On a M1 with 16GB, it was tested that `lab generate` with that limit bumped to
+12GB was able to finish in less than an hour.
+```
+sudo sysctl iogpu.wired_limit_mb=12288
+```
+Once done, make sure to reset the limit back to 0, which resets it to default.
+
+**Note:** This value will reset to defaults after machine reboot.
+
+## `gh` troubleshooting
 
 This page has some troubleshooting techniques if you hit a github cli `gh` error described below.