Re: sysctl -a is slow

On 09/21/10 00:01, David Xu wrote:
> Lawrence Stewart wrote:
>> 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
>>   
> 
> I happened to set kern.sched.preempt_thresh=200, so the kernel is more
> aggressive
> than default on thread preemption. it is easier than default to
> reproduce the
> problem,  my desktop machine is idle, but  it still stalls 1 or 2
> seconds on the sysctl.


heh, from /etc/sysctl.conf on the machine I tested with:

# 4/9/2010
# should give more responsiveness on desktop suggested
# by David Xu <davidxu_at_freebsd.org> on freebsd-stable_at_
kern.sched.preempt_thresh=220

This machine is my primary kde4 desktop at home.

Cheers,
Lawrence