[Bug 269150] bsdconfig: O(n^2) performance in f_device_get_all
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Date: Wed, 25 Jan 2023 16:47:07 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=269150
Bug ID: 269150
Summary: bsdconfig: O(n^2) performance in f_device_get_all
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Some People
Priority: ---
Component: bin
Assignee: bugs@FreeBSD.org
Reporter: asomers@FreeBSD.org
bsdconfig can take a very long time on systems with a large number of disks.
I've seen it take 30 minutes at "Probing devices". top shows that the slowdown
is entirely due to CPU usage of sh, not subprocesses. Inspection shows that
the `f_device_get_all` function calls `f_device_probe_geom` for every geom,
which then calls `f_geom_find`, which again loops over every geom. It's a
classic O(n^2) problem. We need to refactor that code to remove the extra
loops.
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