On 2013-07-05 14:54, Matthew Khouzam wrote: > Quick question. Some traces have overlapping packets, so in that case, > the lost events are between the last event of a previous packet and the > first event of the next packet, which just happens to be the previous > packet's end time? Babeltrace say that the losts are between the beginning of the next and the end of the previous.
> On 13-07-04 06:29 PM, Mathieu Desnoyers wrote: >> * Matthew Khouzam ([email protected]) wrote: >>> Hi tracing werewolves, >>> >>> I want to clear up some stuff about lost events. >>> >>> Lost events are caused, in lttng 2.x when the tracer does not have >>> enough memory available to write an event. This can be due to: >>> * events coming in too fast (faster than we can write them) >>> * a given event being too large >>> * we have an event that does a nested wrap around >>> >>> LTTng will not write the whole packet that is lost. >> LTTng does not write an _event_ discarded at all. However, a packet >> "lost" is a different thing: it only happens in overwrite mode, when we >> overwrite a packet. >> >>> It uses a ring >>> buffer and the packet will just be overwritten in the buffer, but a >>> counter will be incremented. >> For an _event_ discarded, we're not even writing it into the buffer. >> >>> The counter is written in the packet header in the CTF trace. >> Indeed, the event lost counters are written in the packet in the ctf >> trace. >> >>> When reading a trace, if you just read the packet headers, you will see >>> something as follows: >>> >>> Packet 1: >>> ts_begin: 100 >>> ts_end: 200 >>> discarded: 0 >>> >>> Packet 2: >>> ts_begin: 300 >>> ts_end: 400 >>> discarded: 100 >>> >>> Packet 3: >>> ts_begin: 500 >>> ts_end: 600 >>> discarded: 100 >>> >>> Packet 4: >>> ts_begin: 650 >>> ts_end: 750 >>> discarded: 200 >>> >>> With this example, the lost events are located between packets 1, 2 and >>> packets 3,4. >>> >>> If the events are too large, they are discarded in the current packet, >>> lttng does not split events into packets (yet?), and this is lost during >>> a current packet. >>> >>> That means if the events are lost between 1 and 2, they are potentially >>> in the range of [200-400] but probably in [200-300] >>> The next lost event are between 3 and 4 (events discarded is a total >>> count, not local to that packet), so 100 events are also lost between >>> [600-750] but likely in between [600-650]. If you can confirm that all >>> events WITH CONTEXTS are smaller than the packet sizes, I think it's a >>> shoe in that it's between the packets and not containing the next packet. >> "and not contained in the next packet". >> >> Thanks, >> >> Mathieu >> >>> Hope this clarifies some issues, it did for me! >>> >>> Matthew >>> >>> _______________________________________________ >>> lttng-dev mailing list >>> [email protected] >>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev > > _______________________________________________ > lttng-dev mailing list > [email protected] > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
