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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@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
This commit is contained in:
Ivan Nardi 2018-05-31 20:25:08 +02:00 committed by Peter Wu
parent a1a56bd97d
commit 5ff8c3895a
1 changed files with 2 additions and 2 deletions
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4
epan/dissectors/packet-sccp.c
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@ -844,7 +844,7 @@ sccp_reassembly_get_id_pass1(guint32 frame, guint32 offset, guint32 key, gboolea
}
/* Save ID for second pass. */
guint64 *frame_offset = wmem_new(wmem_file_scope(), guint64);
*frame_offset = ((guint64)frame << 32) | offset;
*frame_offset = ((guint64)offset << 32) | frame;
wmem_map_insert(sccp_reassembly_id_map, frame_offset, GUINT_TO_POINTER(id));
return id;
}
@ -852,7 +852,7 @@ sccp_reassembly_get_id_pass1(guint32 frame, guint32 offset, guint32 key, gboolea
static guint32
sccp_reassembly_get_id_pass2(guint32 frame, guint32 offset)
{
guint64 frame_offset = ((guint64)frame << 32) | offset;
guint64 frame_offset = ((guint64)offset << 32) | frame;
return GPOINTER_TO_UINT(wmem_map_lookup(sccp_reassembly_id_map, &frame_offset));
}