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Date: Mon, 20 Sep 2010 14:26:28 +0000
From: David Xu <davidxu@freebsd.org>
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Cc: freebsd-current@freebsd.org
Subject: Re: sysctl -a is slow
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jhell wrote:
> On 09/19/2010 09:28, David Xu wrote:
>> just typed sysctl -a on keyboard, and found it is slow, sometimes
>> it has been stuck for a few seconds, further studied,I found it is
>> stucked at sysctl kern.geom:
>>
>> %/usr/bin/time sysctl -a kern.geom
>> kern.geom.collectstats: 1
>> kern.geom.debugflags: 0
>> kern.geom.label.debug: 0
>> kern.geom.label.ext2fs.enable: 1
>> kern.geom.label.iso9660.enable: 1
>> kern.geom.label.msdosfs.enable: 1
>> kern.geom.label.ntfs.enable: 1
>> kern.geom.label.reiserfs.enable: 1
>> kern.geom.label.ufs.enable: 1
>> kern.geom.label.ufsid.enable: 1
>> kern.geom.label.gptid.enable: 1
>> kern.geom.label.gpt.enable: 1
>>        2.01 real         0.00 user         0.00 sys
>>
>> it seems it needs more than 2 seconds to complete.
>>
> 
> A ktrace(1) and a kdump(1) of the resulting ktrace.out file would
> probably help here along with uname -a. Ive seen this happen once before
> but do not recall what caused it.
> 
> 
> Regards & good luck,
> 

Result is dumped here.
http://people.freebsd.org/~davidxu/sysctl_slow.txt
I think the culprit is sysctl kern.geom.confdot,
which does not appear in normal output, until I check the kdump result.
I tried five times, and it was blocked three times.