[cgl_discussion] libevent & epoll

Frederic Rossi (LMC) Frederic.Rossi at ericsson.ca
Thu Aug 14 07:12:46 PDT 2003


Eric.Chacron at alcatel.fr wrote:

>>To compare what??
>>    
>>
>Simply compare several sw. architectures based on:
>  
>

Do you mean HLR, MGC??  soft real-time or hard real-time??
I don't think we have that kind of tools available for the
targeted workload.

>1) user threads using traditional select() / poll() or SIGIO to get async.
>events
>2) AEM callbacks methods
>3) libevent events called in callback.
>.
>  
>
The problem is to know whether we can handle hundred of thousands of
events and keep the real-time profile of apllications.

The way the callback is executed is not really the issue actually. The
problem is to be able to know how much time it takes to pass the 
information
to the application. We need an upper
bound on the time it takes for the application to get this information.

Also we want to be able to control this value depending on the platform
requirements (real-time...) and priorities associated with the events.

This is the same kind of problems as for deadlines in real-time scheduling
of processes.

I don't say that user space libs are not usefull or efficient, I simply
don't believe that they could solve that problem.

>PS: I saw in your presentation on AEM that "
>No multithreading; Executes user land call-backs
>from kernel space".
>"User call-backs are executed by context-switching the current process"
>I'm not sure to understand how AEM call back is managed ,
>and how many context switch per event.
>
>  
>
An event is (like) a process and must be handle as such. So there is one 
execution
context per event. The context-switch always happens in the context of 
the current
process so this is not a complete context-switch (as for processes).
An event can also create a new process and be detached from the parent 
process.

Frederic

>
>
>
>
>"Frederic Rossi (LMC)" <Frederic.Rossi at ericsson.ca> on 08/14/2003 02:59:34
>PM
>
>To:    Eric CHACRON/FR/ALCATEL at ALCATEL
>cc:    "Randy.Dunlap" <rddunlap at osdl.org>, tabmowzo at us.ibm.com,
>       mika at osdl.org, cgl_discussion at osdl.org
>Subject:    Re: [cgl_discussion] libevent & epoll
>
>
>To compare what?? AEM can be combined with signals, epoll or select.
>
>Each of these mechanisms provides different solutions for different kind of
>problems. Find
>your problem then you will find your solution.
>
>AEM is proposing one solution for Telecom applications running in the
>context of a carrier-grade Linux as described in
>http://aem.sourceforge.net/reports/AEM_cgl_reqts_draft0.6.pdf
>
>Mika:
>At Ottawa (or a few days before) we also said that if your are satisfied
>with epoll+lib, then just use it.
>
>Frederic
>
>
>
>
>
>
>Eric.Chacron at alcatel.fr wrote:
>
>  
>
>>    
>>
>>>I think that I mentioned it several months ago.
>>>My faint recollection of it is that the AEM people said that it's not
>>>sufficient, maybe doesn't do task switching fast enough.
>>>
>>>
>>>      
>>>
>>Is there any benchmark to compare AEM, libevent , POSIX AIO, SIGIO, select
>>/poll  () ...
>>for asynchronous events handling ? Then we 'll have a beter understanding
>>on the added value of each one ...
>>
>>
>>
>>
>>"Randy.Dunlap" <rddunlap at osdl.org>@lists.osdl.org on 08/14/2003 05:15:55
>>    
>>
>AM
>  
>
>>Sent by:    cgl_discussion-admin at lists.osdl.org
>>
>>
>>To:    <tabmowzo at us.ibm.com>
>>cc:    <mika at osdl.org>, <cgl_discussion at osdl.org>
>>Subject:    Re: [cgl_discussion] libevent & epoll
>>
>>
>>
>>
>>    
>>
>>>Mika Kukkonen wrote:
>>>
>>>
>>>      
>>>
>>>>Re: our Ottawa discussion about AEM and a library on top of /dev/epoll
>>>>
>>>>I have a faint recollection that somebody months ago mentioned this:
>>>>       http://monkey.org/~provos/libevent/
>>>>
>>>>Does anybody still remember why it was not an alternative to AEM?
>>>>
>>>>
>>>>        
>>>>
>>>Um, because we forgot it existed?  At least, I don't have any memory of
>>>
>>>
>>>      
>>>
>>it.
>>
>>I think that I mentioned it several months ago.
>>My faint recollection of it is that the AEM people said that it's not
>>sufficient, maybe doesn't do task switching fast enough.
>>
>>~Randy
>>
>>
>>
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