Date: Sat, 30 Dec 2006 19:52:11 +0100 From: Karol Kwiatkowski <freebsd@orchid.homeunix.org> To: Robert Watson <rwatson@freebsd.org> Cc: freebsd-stable@freebsd.org Subject: Re: debugging kernel options Message-ID: <4596B55B.7080506@orchid.homeunix.org> In-Reply-To: <20061230182714.O18740@fledge.watson.org> References: <20061230035722.L39715@thebighonker.lerctr.org> <20061230151933.P18740@fledge.watson.org> <20061230093730.I47579@thebighonker.lerctr.org> <20061230160353.K18740@fledge.watson.org> <45969487.1020806@orchid.homeunix.org> <20061230170358.K50974@fledge.watson.org> <4596AF32.2060205@orchid.homeunix.org> <20061230182714.O18740@fledge.watson.org>
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[-- Attachment #1 --] Robert Watson wrote: > > On Sat, 30 Dec 2006, Karol Kwiatkowski wrote: > >> Robert Watson wrote: >>>> P.S. out of curiosity - now that I have configured kernel with DDB and >>>> KDB options, is there any performance penalty of running such kernel? >>> >>> No, it shouldn't really have any effect on performance. The one >>> thing to watch out for is that your system will no longer reboot >>> automatically on a panic, as it will drop to the debugger, by >>> default. You can change this by setting debug.debugger_on_panic to >>> 0, in which case you will likely want to set debug.trace_on_panic to >>> 1 so it prints a stack trace before rebooting (which is often >>> sufficient, combined with the trap frame and panic message to debug >>> the problem). >>> >>> Right now these are sysctls, not tunables, but you can change the >>> default using options KDB_UNATTENDED (which flips the default to not >>> entering the debugger and rebooting) and options KDB_TRACE (which >>> causes a trace to be printed on panic by default). Probably they >>> should also be tunables so that loader.conf entries will work. >> >> Great explanation, thank you. I turned on debugging on my desktop >> computer which, apart from normal every day use, is 'testing' STABLE >> by running it :) I'm perfectly fine with the defaults, at least for now. > > BTW, if you're running X on your desktop, be aware that it's X that does > all the video mode management. If your box enters the debugger while in > X, the debugger doesn't know how to switch back to text mode (and X > isn't running, obviously), so while you'll be talking to the debugger, > the chances you'll see anything comprehensible are actually quite low. > For this reason, I normally also use a serial console when debugging > desktop boxes: I can always plug my notebook in with a serial cable to > see why it's entered the debugger. Right, I haven't thought about that. I guess without a serial console my best option is to set debug.debugger_on_panic to 0, debug.trace_on_panic to 1 and keep crash dump with kernel.debug for later examination, isn't it? The whole point of doing this, as I am not really experienced in debugging, is to have the information saved somewhere in case of a panic. Regards, Karol -- Karol Kwiatkowski <freebsd at orchid dot homeunix dot org> OpenPGP: http://www.orchid.homeunix.org/carlos/gpg/0x06E09309.asc [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFlrViezeoPAwGIYsRCJ7iAJ0WhekN2ZzjCvoZfkcatgIpgsEZMwCfRFMD Y01GBkYoJgQ6sfOc5e1sNlk= =7f/I -----END PGP SIGNATURE-----
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