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Conn/net_utils/fmt_mac: Avoid snprintf(), memcpy() and allocation

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The fmt_mac() function returning a std::string means the resulting mac
is copied at least once upon returning. Then, the Assign() in GetVal()
taking a std::string internally allocates a new zeek::String which
hits a malloc (no short-string optimization for zeek::String) and then
also copies the content from the std::string into the malloced memory.

Save a few cycles by directly using the allocated memory with the
String instance. This change improves runtime for a SYN-only pcap
with just base/protocols/conn loaded by some 1-2%.
This commit is contained in:
Arne Welzel 2024-02-08 11:32:06 +01:00
parent c41977057a
commit 29f5b507b6
3 changed files with 87 additions and 16 deletions
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12
src/Conn.cc
View file

@ -196,16 +196,20 @@ const RecordValPtr& Connection::GetVal() {
const int l2_len = sizeof(orig_l2_addr);
char null[l2_len]{};
if ( memcmp(&orig_l2_addr, &null, l2_len) != 0 )
orig_endp->Assign(5, fmt_mac(orig_l2_addr, l2_len));
if ( memcmp(&orig_l2_addr, &null, l2_len) != 0 ) {
auto [mac_bytes, mac_len] = fmt_mac_bytes(orig_l2_addr, l2_len);
orig_endp->Assign(5, new String(true, mac_bytes.release(), mac_len));
}
auto resp_endp = make_intrusive<RecordVal>(id::endpoint);
resp_endp->Assign(0, 0);
resp_endp->Assign(1, 0);
resp_endp->Assign(4, resp_flow_label);
if ( memcmp(&resp_l2_addr, &null, l2_len) != 0 )
resp_endp->Assign(5, fmt_mac(resp_l2_addr, l2_len));
if ( memcmp(&resp_l2_addr, &null, l2_len) != 0 ) {
auto [mac_bytes, mac_len] = fmt_mac_bytes(resp_l2_addr, l2_len);
resp_endp->Assign(5, new String(true, mac_bytes.release(), mac_len));
}
conn_val->Assign(0, std::move(id_val));
conn_val->Assign(1, std::move(orig_endp));