On 2019-06-25 15:40:56 [+0200], Jean-Michel Hautbois wrote: > Hi, Hi, > I have a latency issue, and tried to use wakeup_rt latency to detect > it but I am not sure to really understand the output of ftrace... > >From what I understand, the interrupt "irq/28" is having a latency of > ~2ms ?? It sound like a very big latency ! >From the trace, looking only at cpu0 -> - irq/28-c-256 is scheduled until 1581us which 1.5ms. - irq/57-2-122 is scheduled until 2287us another 706us and so on. > And this customer has forced affinity and priorities on its threads, > and I think it could explain such a behaviour ? For instance the task > named "tLaserLo-762" is in fact forced with an affinity of 2 and a > priority of SCHED_FIFO 30. > > https://framabin.org/p/?e63c638b5cf2e4ec#GS6ahFDEI/m6vyY2lwafB96vbgA4Skft1d+Dvtry2QI= it is not the nicest pastebin page to grab the bare text file from… > I think it gives a very nice example of what preemption really is, but > it can be confusing. > Can it be traced with kernelshark or something else ? you could try to trace with kernelshark and enable the scheduling events. You should be able to see when a task is woken up and when it finally got on the CPU. And then you can decide what to do. > Thanks, > JM Sebastian
