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monitor: Reduce handle_qmp_command() tracing overhead

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We are malloc'ing a QString and spending CPU cycles on converting a
QObject to string, just for the sake of sticking the string in the trace
message.  Wasted when we aren't tracing.  Avoid that.

[Commit message and description suggested by Markus Armbruster to
provide more detail about the rationale for this patch.

Use trace_event_get_state_backends() instead of trace_event_get_state()
to honor DTrace/UST backend dstates.
--Stefan]

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20170725143923.11241-1-den@openvz.org
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Lluís Vilanova <vilanova@ac.upc.edu>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Denis V. Lunev 2017-07-25 17:39:23 +03:00 committed by Stefan Hajnoczi
parent 8908eb1a4a
commit bd6952a391
1 changed files with 5 additions and 4 deletions
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9
monitor.c
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@ -3823,7 +3823,6 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
QDict *qdict = NULL;
Monitor *mon = cur_mon;
Error *err = NULL;
QString *req_json;
req = json_parser_parse_err(tokens, NULL, &err);
if (!req && !err) {
@ -3841,9 +3840,11 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
qdict_del(qdict, "id");
} /* else will fail qmp_dispatch() */
req_json = qobject_to_json(req);
trace_handle_qmp_command(mon, qstring_get_str(req_json));
QDECREF(req_json);
if (trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
QString *req_json = qobject_to_json(req);
trace_handle_qmp_command(mon, qstring_get_str(req_json));
QDECREF(req_json);
}
rsp = qmp_dispatch(cur_mon->qmp.commands, req);