Re: textdumps are too slow

On Thu, Apr 6, 2023 at 9:08 AM Alan Somers <asomers@freebsd.org> wrote:
>
> I have servers with lots of RAM yet slow swap disks.  So full crash
> dumps are too slow.  Instead, I use textdumps, which are theoretically
> much faster.  However, these servers also have about 10,000 threads
> apiece, so textdumps are also slow.  They take tens of minutes.  I
> have dual console setup: both serial and video.  It seems to me that
> the speed of the textdump might be limited by the video system.  So is
> there anyway to capture a textdump without printing everything to the
> console?  textdump(4) implies that there isn't; you must print stuff
> to console in order to capture it, and you must capture in order to
> dump.  Would somebody please tell me that I'm wrong?
>
> -Alan

I'll answer my own question.  It turns out that ddb can mute the
console, just like "conscontrol mute on" would.  That makes textdumps
much much faster.  The command is "write cn_mute 1".  So to use this
trick, write the following to /etc/ddb.conf:

script kdb.enter.panic=textdump set; capture on; write cn_mute 1; run
lockinfo; show pcpu; bt; ps; alltrace; capture off; textdump dump;
reset