real time question : RR vs FF?

Michael Trimarchi michael at
Sun May 1 23:47:08 PDT 2011

On 05/01/2011 05:54 PM, Victor henri wrote:
> Hello Stefan and thank you for your answer
>>> It was quite easy to find...
>>> In the 'testrtpool.c' file, in the 'default-push' function, I just had to
>>> replace "SCHED_RR" by "SCHED_FIFO"
>>> On the other hand, 'param.sched_priority' is set to to 50, which can be changed
>>> also according to the priority one wants to give to the process;
>> I hope you have a good reason for using SCHED_FIFO. 1st I hope you understand
>> that you will only get scheduling priority, I you are not running fast enough,
>> this is *not* the solution
> My app is very demanding since it involves realtime (and very fast) analysis and display of the data's. Although my machine is powerfull enough, I suppose that on machine that are not powerfull enough, this could cause lock up.
> . 2nd I hope you understand the dangers of SCHED_FIFO
>> vs. SCHED_RR.
> As far as I know, the  main difference is that the SCHED_FIFO cannot be prempted 
> unless another process of higher priority shows up in the execution 
> queue; and
> SCHED_RR can be preempted by a time quantum... 

Can you give a try to SCHED_DEADLINE for your application?

Michael Trimarchi

> I apreciate your warning and get back to the RR policy for now and investigate more. Indeed it may be more safe.
> Thank you so much for sharing
> Victor
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| Michael Nazzareno Trimarchi                     Amarula Solutions BV |
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