[Freeswitch-dev] On high CPU usage and NONBLOCK-ed sockets

[Oleg Khovayko]

Another idea to conserve CPU and sys-time usage - to use adaptive 
timeouts in the timewait intervals.
General idea: requests to our system aren't random, but correlated. For 
example, night time
there are too few requests, and so on.

Simple code for demonstrate algorithm following.
There is min_interval is ~4ms, max_interval is ~524ms:


uint32_t interval = 1 << 25; // ~4ms

while(usleep(interval >> 13)) { // Max 2^19us, or 524ms
    // wake up here
    if(need_to_do_something) {
      do_something();
      interval = 1 << 25; // Reset interval
    } else {
       // Nothing to do -- *2 interval
       interval |= interval << 1;
    }
}



Anthony Minessale wrote:
> Can you produce some example code that we can test on other architectures?
> What exactly were you doing in mod_skinny? if you copied
> mod_event_socket it may be true your blocking approach is better but
> mod_event_socket has some high performance reasons to not block.
>
> We use the centos kernel and trying to make it work better on debian
> with a newer kernel could disrupt our stable user base.
>
> consider making a mod_debug or mod_testperf we can mess with on many boxes.
>
>
>
> On Fri, Sep 3, 2010 at 3:52 PM, Mathieu Parent<math.parent at gmail.com>  wrote:
>    
>> On Fri, Sep 3, 2010 at 8:22 PM, Anthony Minessale
>> <anthony.minessale at gmail.com>  wrote:
>>      
>>> What do you mean by high cpu exactly?
>>>        
>> when going blocking-mode, the user CPU gets lower and the kernel CPU is similar.
>>
>>      
>>>   what are you using to measure it?
>>>        
>> top, vmstat
>>
>> without mod_skinny
>> mathieu at netthieu:~/apps/freeswitch/freeswitch.git$ vmstat 5 5
>> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
>>   r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
>>   7  0     48 175552 161664 787636    0    0     8    10  184  361  6  8 86  1
>>   1  0     48 171948 161672 791372    0    0     0     5 4141 9191 14 12 74  0
>>   0  0     48 171700 161684 791496    0    0     0    11 4125 9081 13  9 78  0
>>   0  0     48 175048 161688 787860    0    0     0     3 4344 9177  7 10 84  0
>>   6  0     48 175048 161692 787860    0    0     0     1 4225 9035  9 11 80  0
>>
>> with mod_skinny NONBLOCKED
>> mathieu at netthieu:~/apps/freeswitch/freeswitch.git$ vmstat 5 5
>> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
>>   r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
>>   1  0     48 172668 162104 789052    0    0     8    10  190  374  6  8 86  1
>>   1  0     48 173528 162108 788652    0    0     0     2 4792 10346 15 13 72  0
>>   1  0     48 173528 162124 788664    0    0     0    17 4678 10326  9 12 78  0
>>   0  0     48 173528 162124 788628    0    0     0     1 4788 10343 10 14 77  0
>>   9  0     48 166956 162136 792764    0    0     0    10 4592 10535 16 13 71  0
>>
>> with mod_skinny BLOCKED
>> mathieu at netthieu:~/apps/freeswitch/freeswitch.git$ vmstat 5 5
>> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
>>   r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
>>   0  0     48 175288 161648 787832    0    0     8    10  182  358  6  8 86  1
>>   1  0     48 175280 161648 787824    0    0     0     0 4236 9054  7  9 83  0
>>   7  0     48 175404 161648 787804    0    0     0     3 4173 8927  7 10 83  0
>>   0  0     48 175280 161652 787576    0    0     0     5 4288 9182  9 10 81  0
>>   6  0     48 175404 161656 787580    0    0     0     4 4209 9001  8 10 82  0
>>
>> So it seems that both %user and %system are lower. I have not done
>> complete tests but mod_skinny is more responsive in BLOCKING-mode
>>
>>      
>>> what OS are you on?
>>>        
>> Linux netthieu 2.6.32-5-686 #1 SMP Thu Aug 12 13:38:27 UTC 2010 i686 GNU/Linux
>>
>> this is Debian testing using FS built from recent git using debian packaging.
>>
>>
>>      
>>> in my findings not more efficient, not at all reliable.
>>>        
>> Googling some, I found (from
>> http://www.ibm.com/developerworks/linux/library/l-async/)
>>
>> "Synchronous non-blocking I/O: A less efficient variant of synchronous
>> blocking". This is what we are doing?
>>
>> The good solutions IMO are:
>> - Synchronous blocking I/O: simple and efficient
>> - Asynchronous blocking I/O: not so good. use of "select" is not recommended
>> - Asynchronous non-blocking I/O (AIO) which is a completely different
>> API (portable?) which should fit well with FS's event model but with a
>> lot of work
>>
>> Maybe we can make it configurable at build-time (as it is in
>> mod_skinny) to allow performance testing? Perhaps the results will be
>> very different from one platform to another.
>>
>> Mathieu
>>
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>>      
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