Eric Lee / smarc-fsl-linux-kernel

21 Nov, 2019

1 commit

21 May, 2019

1 commit

06 Nov, 2018

1 commit

  • ebd09753b   nds32: Perf porting ... Browse Code »

    This is the commit that porting the perf for nds32.

    1.Raw event:
    The raw events start with 'r'.
    Usage:
    perf stat -e rXYZ ./app
    X: the index of performance counter.
    YZ: the index(convert to hexdecimal) of events

    Example:
    'perf stat -e r101 ./app' means the counter 1 will count the instruction
    event.

    The index of counter and events can be found in
    "Andes System Privilege Architecture Version 3 Manual".

    Or you can perform the 'perf list' to find the symbolic name of raw events.

    2.Perf mmap2:

    Fix unexpected perf mmap2() page fault

    When the mmap2() called by perf application,
    you will encounter such condition:"failed to write."
    With return value -EFAULT

    This is due to the page fault caused by "reading" buffer
    from the mapped legal address region to write to the descriptor.
    The page_fault handler will get a VM_FAULT_SIGBUS return value,
    which should not happens here.(Due to this is a read request.)

    You can refer to kernel/events/core.c:perf_mmap_fault(...)
    If "(vmf->pgoff && (vmf->flags & FAULT_FLAG_WRITE))" is evaluated
    as true, you will get VM_FAULT_SIGBUS as return value.

    However, this is not an write request. The flags which indicated
    why the page fault happens is wrong.

    Furthermore, NDS32 SPAv3 is not able to detect it is read or write.
    It only know either it is instruction fetch or data access.

    Therefore, by removing the wrong flag assignment(actually, the hardware
    is not able to show the reason), we can fix this bug.

    3.Perf multiple events map to same counter.

    When there are multiple events map to the same counter, the counter
    counts inaccurately. This is because each counter only counts one event
    in the same time.
    So when there are multiple events map to same counter, they have to take
    turns in each context.

    There are two solution:
    1. Print the error message when multiple events map to the same counter.
    But print the error message would let the program hang in loop. The ltp
    (linux test program) would be failed when the program hang in loop.

    2. Don't print the error message, the ltp would pass. But the user need to
    have the knowledge that don't count the events which map to the same
    counter, or the user will get the inaccurate results.

    We choose method 2 for the solution

    Signed-off-by: Nickhu
    Acked-by: Greentime Hu
    Signed-off-by: Greentime Hu

    Nickhu
     

22 Feb, 2018

2 commits