lkml.org 
[lkml]   [2009]   [May]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 3/5] perf_counter: rework ioctl()s
    Paul Mackerras wrote:
    > Corey Ashford writes:
    >
    >> Another hypothesis is that the old PAPI code would open, mmap, close,
    >> then reopen, and mmap again. I wonder if because I wasn't munmap'ing
    >> before the close, that I got some strange behavior from the kernel.
    >
    > In general an mmap will keep a reference to the file it is mapping,
    > which means that if you do an mmap on a fd and then close the fd, the
    > file stays open until the region is munmapped. So your old PAPI code
    > would have ended up with more counters active than you expected, if
    > you thought closing the fd would have destroyed the counter.
    >
    > That is, you don't have to munmap before close, but you do have to do
    > both close and munmap to destroy the counter.


    That makes perfect sense. I'll bet that's what the problem was. I think this
    issue can be closed. Thank you Paul M. and Peter Z. for looking into this.

    - Corey



    \
     
     \ /
      Last update: 2009-05-13 00:55    [W:0.020 / U:1.392 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site