Re: sysctl -a is slow

On 09/21/10 02:21, David Xu wrote:
> jhell wrote:
>>
>> On Mon, 20 Sep 2010 10:26, David Xu wrote:
>> In Message-Id: <4C976F14.8000408_at_freebsd.org>
>>
>>> 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.
>>>
>>
>>
>> Inspecting the output of sysctl -b kern.geom.confdot will give you
>> what you currently have configured in the system as disks and what not
>> through geom. If this seems to be bailing at that point, which is an
>> opaque MIB/OID which doesn't come up other than when you use the "-o"
>> switch to sysctl(1) then could you check your labels for your disks
>> for any weird characters in the labels ?
>>
>> ( sysctl -bo kern.geom )
>>
>> Also does this have the same effect when run in a xterm, cons25
>> terminal ?
>>
>> And same for the above but with the C, *_COUNTRY.UTF-8 or your normal
>> locale ?
>>
>> ( env LANG=C sysctl kern.geom )
>>
>> Looking at the output from mine there are quite a few unprintable
>> characters present. Maybe these are having an impact with one of your
>> labels.
>>
>>
> 
> I redirect all output to a disk file, and it still needs 1 second to
> complete, this machine is dual-core pentium E5500, faster than previous
> one which is a dual-core AMD 5000+ machine, the 5000+ needs 2
> seconds to complete.
> 
> $/usr/bin/time sysctl -b kern.geom.confdot > sysctl_geom_confdot.txt
>         1.00 real         0.00 user         0.00 sys
> 
> the file is here:
> http://people.freebsd.org/~davidxu/sysctl_geom_confdot.txt

As an extra data point, running "/usr/bin/time sysctl -b
kern.geom.confdot" repeatedly on my amd64 8.1-STABLE desktop varies
between 0s and 2s. It reports 0 majority of the time but every 5 or so
runs it'll stall for 1 or 2 seconds. So the problem isn't isolated to head.

Cheers,
Lawrence