Wireshark · Wireshark-commits: [Wireshark-commits] master 5ff8c38: SCCP: fix performance drop in reassembler code

[Wireshark code review <code-review-do-not-reply@xxxxxxxxxxxxx>]

URL: https://code.wireshark.org/review/gitweb?p=wireshark.git;a=commit;h=5ff8c3895a41b44486fbc17e05e4a188e3c4827e
Submitter: Peter Wu (peter@xxxxxxxxxxxxx)
Changed: branch: master
Repository: wireshark

Commits:

5ff8c38 by Ivan Nardi (nardi.ivan@xxxxxxxxx):

    SCCP: fix performance drop in reassembler code
    
    Commit 46dc5f75, while fixing sccp reassembler in the generic case, introduced
    a huge performance drop in some scenarios.
    The bottleneck is the sccp_reassembly_id_map hash table and, more precisely,
    the combination of the key layout and the hash function g_int64_hash()
    The key is defined as:
        guint64 key = ((guint64)frame << 32) | offset;
    Since the hash function uses only the lowest 32 bits of the key, all fragments
    at the same offset are saved in the same bucket
    
    If the sccp fragments are always in different packets and at the same offset
    (because, for example, there are only 1 chunk in every sctp packet) the hash
    table degenerates in exactly one linked list.
    
    Changing the key definition seems to restore the original performance
    
    Since there are usually hardly more than ~10/20 sctp chunks in a packet,
    this change shouldn't significantly affect performance when (all) fragments
    are in the same frame
    
    Change-Id: I2867a72819c2d91e1e0ae2cb97d63b5684d35bcc
    Reviewed-on: https://code.wireshark.org/review/27944
    Petri-Dish: Peter Wu <peter@xxxxxxxxxxxxx>
    Tested-by: Petri Dish Buildbot
    Reviewed-by: Peter Wu <peter@xxxxxxxxxxxxx>
    

Actions performed:

    from  a1a56bd   Qt: Move Layout and clear master_split use
    adds  5ff8c38   SCCP: fix performance drop in reassembler code


Summary of changes:
 epan/dissectors/packet-sccp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)