On 14-02-17 11:21 AM, Mathieu Desnoyers wrote: > I'm seeing here that the event in trace_marker is limited to 1 page (it can > cross a page boundary, so ftrace deals with 2 pages at most). It makes sense, > since Ftrace's buffers are split into pages. > > Its truncation happens here: > > if (cnt > TRACE_BUF_SIZE) > cnt = TRACE_BUF_SIZE;
Good to know. So at least we know ftrace truncates by default. > The minimum size of sub-buffers (trace packets) LTTng can allocate is a page. > However, the available space for event records is slightly less, since we have > a packet header at the beginning of the packet. Since the packet header can > be extended between LTTng versions, it's hard to say. The space can be > slightly less if event contexts are enabled (this can be done dynamically > at runtime, per-buffer). > > Thoughts ? I'd be tempted to say that anything that big should be good enough. But from the sounds of it, even doing strlen's in user-space wouldn't be good enough to ensure that the data fits in lttng buffer. I can't say that I have a good solution here. Ideally there should be some form of automatic truncation somewhere without having to go through the expense of strlens or the likes. -- Karim Yaghmour CEO - Opersys inc. / www.opersys.com http://twitter.com/karimyaghmour _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
