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Commits on Nov 11, 2010
  1. oprofile fix for hashing backtraces.

    Mike Dodd authored
    Oprofile's hash function uses a 64-bit value for the
    key where the high 32-bit are the 'from' address in a backtrace,
    and the low 32-bits are the current PC. However, the hash
    function was:
      uint32_t temp = (value >> 32) ^ value;
      return ((temp << 0) ^ (temp >> 8)) & data->hash_mask;
    If 'from' and 'to' are the same (recursive function), this hashes
    to 0, and you end up with lots of collisions, turning the
    theoretically O(1) operation into O(n).
    To fix it, I just drop the high 32-bits from the hash:
      uint32_t temp = value & 0xffffffff;
      return ((temp << 0) ^ (temp >> 8)) & data->hash_mask;
    In testing, this drastically reduces the oprofile overhead
    for some tracing.
    Change-Id: I8ae65a8a73771c89b576c895f135efd7b730eaf5
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