Too Much Context Switching?

[Kris Kennaway]

alex at schnarff.com wrote:
> Quoting Kris Kennaway <kris at FreeBSD.org>:
> 
>> Michel Talon wrote:
>>> On Mon, Jun 30, 2008 at 07:53:00PM +0200, Kris Kennaway wrote:
>>>> Yep, it could be that -- what confuses me though is that it is 
>>>> claimed that performance suddenly regressed.  If so then this cannot 
>>>> be the underlying cause.
>>>
>>> It may be that the load has augmented to the point that contention
>>> imposes a rapid regression on throughput.
>>
>> Yes, it could be that.  I don't know off-hand whether multiple threads
>> are counted separately by vmstat (at a guess I'd say no), but ps/top/etc
>> should show how many are active in the python process.
> 
> Just ran ktrace, and a bit of Googling seems to confirm my initial 
> suspicion that the results I'm seeing are abnormal. The first several 
> screenfulls of output look like this:
> 
>  52929 python2.4 1214867016.469416 CALL  kse_wakeup(0x811740c)
>  52929 python2.4 0.000060 RET   kse_wakeup 0
>  52929 python2.4 0.000008 RET   kse_release 0
>  52929 python2.4 0.000040 CALL  kse_release(0x811df4c)
>  52929 python2.4 0.000515 CALL  kse_wakeup(0x811740c)
>  52929 python2.4 0.000012 RET   kse_wakeup 0
>  52929 python2.4 0.000004 RET   kse_release 0
>  52929 python2.4 0.000012 CALL  kse_release(0x811df4c)
>  52929 python2.4 0.000365 CALL  kse_wakeup(0x811740c)
>  52929 python2.4 0.000012 RET   kse_wakeup 0
>  52929 python2.4 0.000003 RET   kse_release 0
>  52929 python2.4 0.000010 CALL  kse_release(0x811df4c)
>  52929 python2.4 0.000413 CALL  kse_wakeup(0x811740c)
>  52929 python2.4 0.000011 RET   kse_wakeup 0
>  52929 python2.4 0.000004 RET   kse_release 0
>  52929 python2.4 0.000009 CALL  kse_release(0x811df4c)
>  52929 python2.4 0.000393 CALL  kse_wakeup(0x811740c)
>  52929 python2.4 0.000012 RET   kse_wakeup 0
>  52929 python2.4 0.000004 RET   kse_release 0
>  52929 python2.4 0.000009 CALL  kse_release(0x811df4c)
> 
> I may be mistaken, but it seems like that's a lot of unnecessary 
> activity managing the threads; the confirmation I found came from 
> http://arkiv.freebsd.se/?ml=freebsd-threads&a=2007-02&t=3178634.
> 
> Am I correct that this is abnormal behavior? If so, any idea what I may 
> need to do to fix the issue?

Looks exactly like the python thread problem Michel described.

You will get some improvement by switching to libthr and/or updating to 
7.0 as I discussed, but ultimately you're hitting limits of python, not 
FreeBSD.

Kris