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PROCESSOR-SDK-AM62X: What is the qos of the linux-rt system, and what is its function?

Katherine Wang
Intellectual 2210 points
Part Number: PROCESSOR-SDK-AM62X

Hi Team,

At present, I am testing the real-time performance of linux-rt. Using Forlinx's image (based on sdk08.03.00.19) and the official SDK08-04-01-03, I compiled this image on Forlinx's board.


My problem is that during the test, I used the cyclictest command on sdk08.04 to test the real-time performance, and an error would be reported, saying that dev/cpu_dma_latency cannot be found.

However, no error was reported in the test on Feiling's board.

I analyzed them and found that dev/cpu_dma_latency error was reported by the qos.c file.

As shown in the figure below, the qos on the left is not binary, that is, it is not compiled into the kernel.

However, for the official 08.04 version sdk on the right, it is compiled into it.
Could you please tell me what qos is and what its functions are? How is dev/cpu_dma_latency generated?

Kind regards,

Katherine

  • 0
    TI__Mastermind 27050 points

    Hi,

    The /dev/cpu_dm_latency Warning (not error) is related to the power management qos framework, and cyclictest is trying to disable it by writing zero to the file. In the current SDK release the power management framework is not configured on, which results in the file not existing. For interrupt latency purposes and real-time one would usually disable any complex power management to get a better interrupt response. So for cyclictest purposes the Warning can be ignored. If you build the kernel with power management framework the file will be there. 

    Once the low power states and resume suspend become available in AM62x SDK this will change, but for RT purposes and best performance of worst case interrupt latency (use case cyclistest is used for) typically power management would be off.

      Pekka