----- Original Message ----- > From: "Karim Yaghmour" <[email protected]> > To: "Mathieu Desnoyers" <[email protected]> > Cc: [email protected] > Sent: Monday, February 17, 2014 11:26:26 AM > Subject: Re: [RFC PATCH lttng-modules] LTTng logger ABI > > > 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.
trace.h:#define TRACE_BUF_SIZE 1024 so actually, ftrace truncates at 1024 bytes. We could very well do the same within the lttng-logger write() op. Thoughts ? Thanks, Mathieu > > -- > Karim Yaghmour > CEO - Opersys inc. / www.opersys.com > http://twitter.com/karimyaghmour > > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
