• A
    perf symbols: Use the buildids if present · 8d06367f
    Arnaldo Carvalho de Melo 提交于
    With this change 'perf record' will intercept PERF_RECORD_MMAP
    calls, creating a linked list of DSOs, then when the session
    finishes, it will traverse this list and read the buildids,
    stashing them at the end of the file and will set up a new
    feature bit in the header bitmask.
    
    'perf report' will then notice this feature and populate the
    'dsos' list and set the build ids.
    
    When reading the symtabs it will refuse to load from a file that
    doesn't have the same build id. This improves the
    reliability of the profiler output, as symbols and profiling
    data is more guaranteed to match.
    
    Example:
    
     [root@doppio ~]# perf report | head
     /home/acme/bin/perf with build id b1ea544ac3746e7538972548a09aadecc5753868 not found, continuing without symbols
      # Samples: 2621434559
      #
      # Overhead          Command                  Shared Object  Symbol
      # ........  ...............  .............................  ......
      #
           7.91%             init  [kernel]        [k] read_hpet
           7.64%             init  [kernel]        [k] mwait_idle_with_hints
           7.60%          swapper  [kernel]        [k] read_hpet
           7.60%          swapper  [kernel]        [k] mwait_idle_with_hints
           3.65%             init  [kernel]        [k] 0xffffffffa02339d9
    [root@doppio ~]#
    
    In this case the 'perf' binary was an older one, vanished,
    so its symbols probably wouldn't match or would cause subtly
    different (and misleading) output.
    
    Next patches will support the kernel as well, reading the build
    id notes for it and the modules from /sys.
    
    Another patch should also introduce a new plumbing command:
    
    'perf list-buildids'
    
    that will then be used in porcelain that is distro specific to
    fetch -debuginfo packages where such buildids are present. This
    will in turn allow for one to run 'perf record' in one machine
    and 'perf report' in another.
    
    Future work on having the buildid sent directly from the kernel
    in the PERF_RECORD_MMAP event is needed to close races, as the
    DSO can be changed during a 'perf record' session, but this
    patch at least helps with non-corner cases and current/older
    kernels.
    Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Frank Ch. Eigler <fche@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Jason Baron <jbaron@redhat.com>
    Cc: Jim Keniston <jkenisto@us.ibm.com>
    Cc: K. Prasad <prasad@linux.vnet.ibm.com>
    Cc: Masami Hiramatsu <mhiramat@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    LKML-Reference: <1257367843-26224-1-git-send-email-acme@infradead.org>
    Signed-off-by: NIngo Molnar <mingo@elte.hu>
    8d06367f
header.h 1.5 KB