Take  a look in your FS logs..
Im pretty sure you will see the whimsical & Awesome log message :

LUKE: I'm hit, but not bad.
LUKE'S VOICE: Artoo, see what you can do with it. Hang on back there....

this is in thread_launch_failure in switch_core_session.c ( around line 1714 )
and around this code you can easily see the following 

sess_count = switch_core_session_count();
if (sess_count > 110) {
switch_core_session_limit(sess_count - 10);

as you can see, it bumps 10 off your SPS, every time thread_launch_failure is called.

thread_launch_failure is called whenever switch_thread_create fails to create a thread.
which basically means apr_thread_create 

I have seen this myself with MUCH lower SPS on openVZ machines, but since your seeing it also im now hoping we can nut this out :)
im going to dig a little more and see what I can find.

what openVZ kernel are you using out of interest ?
ive seen this on a fairly old, but stable 2.6.32-19-pve

let me know what you find ! 





On 28 March 2014 04:30, Muhammad Naseer Bhatti <nbhatti@gmail.com> wrote:
Yes, i was thinking on same lines. Its running over OpenVZ kernel.
I am now going to try replicate this in a physical env.

Sent from my iPad

> On Mar 27, 2014, at 9:11 PM, William King <william.king@quentustech.com> wrote:
>
> Is your FS instance running in a virtual environment?
>
> William King
> Senior Engineer
> Quentus Technologies, INC
> 1037 NE 65th St Suite 273
> Seattle, WA 98115
> Main:   (877) 211-9337
> Office: (206) 388-4772
> Cell:   (253) 686-5518
> william.king@quentustech.com
>
>> On 03/27/2014 11:07 AM, Muhammad Naseer Bhatti wrote:
>> No i am definitely not going to that SPS limit. The peak was set to 400
>> so maybe this is just a skewed value. 1000 session does not look to be
>> high load. The call is bridged and set to play silence and disconnects
>> at random time under 1 minute.  The resources on the server also clearly
>> seem to be available. I am not gearing this towards a how do i ....
>> Performance kind of a thread but could there be something unusual here?
>>
>> Sent from my iPad
>>
>> On Mar 27, 2014, at 9:07 PM, Ken Rice <krice@freeswitch.org
>> <mailto:krice@freeswitch.org>> wrote:
>>
>>> Re: [Freeswitch-users] FreeSWITCH changing max_sessions automatically
>>> You’re hitting a melt down protection... Once it reaches a limit and
>>> cant allocate the additional resources for creating anew session it
>>> will back down the max sessions limit to help save itself...
>>>
>>> The PEAK SPS there was a value seen at some point the SPS buffer...
>>> Depending on you beating the machine to death it is possible that
>>> number got skewed due to a timer miss
>>>
>>>
>>> On 3/27/14 10:57 AM, "Muhammad Bhatti" <nbhatti@gmail.com> wrote:
>>>
>>>
>>>    Just have noticed something new today. Testing a local instance on
>>>    CentOS 6.0 with FreeSWITCH Version 1.2.23~64bit. FreeSWITCH seems
>>>    to be changing the max_sessions param automatically. This happens
>>>    when typically I bridge around 1000 sessions and whatever value I
>>>    set to sps and max_sessions, it comes down.
>>>
>>>    UP 0 years, 0 days, 0 hours, 37 minutes, 54 seconds, 362
>>>    milliseconds, 294 microseconds
>>>    FreeSWITCH (Version 1.2.23  64bit) is ready
>>>    74716 session(s) since startup
>>>     *976 session(s) - peak 1022, last 5min 985
>>>    112 session(s) per Sec out of max 400, peak 9053, last 5min 317 <-
>>>    BTW This peak was never tried, not sure why it says 9053
>>>     5000 session(s) max
>>>    min idle cpu 0.00/55.00
>>>    Current Stack Size/Max 240K/8192K
>>>
>>>    =======
>>>    followed by
>>>    =======
>>>
>>>    switch_core_session.c:2288 Over Session Limit! 1013
>>>    mod_sofia.c:4884 Error Creating Session
>>>
>>>    =======
>>>    And then
>>>    =======
>>>
>>>    freeswitch@internal> status
>>>    UP 0 years, 0 days, 0 hours, 38 minutes, 35 seconds, 372
>>>    milliseconds, 831 microseconds
>>>    FreeSWITCH (Version 1.2.23  64bit) is ready
>>>    76231 session(s) since startup
>>>     560 session(s) - peak 1023, last 5min 1023
>>>    0 session(s) per Sec out of max 400, peak 9053, last 5min 317
>>>     1013 session(s) max
>>>    min idle cpu 0.00/99.00
>>>    Current Stack Size/Max 240K/8192K
>>>
>>>
>>>    Is this something changed recently? Or some sort of server
>>>    meltdown protection mechanism being forked :)
>>>
>>>
>>>    *
>>>
>>> *
>>> *--
>>> Ken
>>> _http://www.FreeSWITCH.org
>>> http://www.ClueCon.com
>>> http://www.OSTAG.org
>>> _irc.freenode.net <http://irc.freenode.net> #freeswitch
>>> Twitter: @FreeSWITCH
>>>
>>> _________________________________________________________________________
>>> Professional FreeSWITCH Consulting Services:
>>> consulting@freeswitch.org <mailto:consulting@freeswitch.org>
>>> http://www.freeswitchsolutions.com
>>>
>>> FreeSWITCH-powered IP PBX: The CudaTel Communication Server
>>> http://www.cudatel.com
>>>
>>> Official FreeSWITCH Sites
>>> http://www.freeswitch.org
>>> http://wiki.freeswitch.org
>>> http://www.cluecon.com
>>>
>>> FreeSWITCH-users mailing list
>>> FreeSWITCH-users@lists.freeswitch.org
>>> <mailto:FreeSWITCH-users@lists.freeswitch.org>
>>> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
>>> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
>>> <http://lists.freeswitch.org/mailman/options/freeswitch-users>
>>> http://www.freeswitch.org
>>
>>
>> _________________________________________________________________________
>> Professional FreeSWITCH Consulting Services:
>> consulting@freeswitch.org
>> http://www.freeswitchsolutions.com
>>
>> FreeSWITCH-powered IP PBX: The CudaTel Communication Server
>> http://www.cudatel.com
>>
>> Official FreeSWITCH Sites
>> http://www.freeswitch.org
>> http://wiki.freeswitch.org
>> http://www.cluecon.com
>>
>> FreeSWITCH-users mailing list
>> FreeSWITCH-users@lists.freeswitch.org
>> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
>> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
>> http://www.freeswitch.org
>>
>
> _________________________________________________________________________
> Professional FreeSWITCH Consulting Services:
> consulting@freeswitch.org
> http://www.freeswitchsolutions.com
>
> FreeSWITCH-powered IP PBX: The CudaTel Communication Server
> http://www.cudatel.com
>
> Official FreeSWITCH Sites
> http://www.freeswitch.org
> http://wiki.freeswitch.org
> http://www.cluecon.com
>
> FreeSWITCH-users mailing list
> FreeSWITCH-users@lists.freeswitch.org
> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
> http://www.freeswitch.org

_________________________________________________________________________
Professional FreeSWITCH Consulting Services:
consulting@freeswitch.org
http://www.freeswitchsolutions.com

FreeSWITCH-powered IP PBX: The CudaTel Communication Server
http://www.cudatel.com

Official FreeSWITCH Sites
http://www.freeswitch.org
http://wiki.freeswitch.org
http://www.cluecon.com

FreeSWITCH-users mailing list
FreeSWITCH-users@lists.freeswitch.org
http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
http://www.freeswitch.org



--
Sincerely

Jay