[lttng-dev] [GIT PULL v3] Accounting packet lost and discarded events at runtime

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Sun Aug 2 11:38:25 EDT 2015

----- On Aug 1, 2015, at 11:41 PM, Julien Desfossez jdesfossez at efficios.com wrote:

> This patchset is composed of commits in lttng-tools, lttng-ust and
> lttng-modules, it allows the sessiond, to report to the user the
> discarded events (when a channel is in discard mode) or the lost packets
> (when a channel is in overwrite mode).
> Please pull from:
> https://github.com/jdesfossez/lttng-tools-dev/tree/seqnum
> a312e89 Store the instance id and packet_seq_num in indexes
> e40456e kernctl commands to extract the stream instance id
> 53d9b1d Account the lost packets in snapshot mode
> 17d0d29 Display discarded and lost events at destroy and stop
> 291246b Extract the lost packets and discarded events counters
> 0965b2f Metadata for instance_id and packet_seq_num
> a0badfd Reference pointers from ust_app_chan to parent structs
> 082f79d Explicitly stop the session on lttng destroy
> https://github.com/jdesfossez/lttng-modules-dev/tree/seqnum
> fa326dd Add stream instance id to the packet header
> cf556ea Add a packet sequence number

Just merged those two commits into lttng-modules master.
They don't have locked-step requirements with tools.

> https://github.com/jdesfossez/lttng-ust-dev/tree/seqnum
> 66eb100 Export the stream instance ID
> 72d75d7 Generate and export the sequence number
> 885e9ba Add stream instance id to the packet header

Reviewed those commits. At this point, after taking care of
the last comments, each should have my acked-by. However, those
need to wait until Jeremie can review the tools changes, because
those need to be done in locked-step.

Are there any changes required in Babeltrace associated with the
new packet context fields ?



> Since we are in the last sprint of the 2.7 release, I will try to keep
> these branches up-to-date by rebasing regularly until the maintainers
> have some time to review and merge into master, so the commit IDs might
> change, but the commit messages won't. I can resubmit as emails instead
> of a pull request if it is easier for the review.
> Change from v2:
> - actually pushed the updates intended for v1 in UST and tools...
> - fixed the comments from Mathieu on the v2
> Change from v1:
> - the packet sequence number is not dependant on the subbuf_size and now
> always a uint64_t, so it got rid of the need of the
> packet_seq_num_padding field
> Original cover letter:
> The reporting is detailled on a per-channel basis in the "lttng list"
> command (and associated API calls) at runtime. On lttng stop/destroy, a
> warning is now displayed to the user if events/packets were
> discarded/lost during the session.
> The information about the packet lost is extracted from a packet
> sequence number now written in each CTF packet and CTF index, allowing
> the relayd and the viewers to know when parsing the trace/index that
> entire packets were lost between two data packets.
> Finally, a stream_instance_id is now written in each packet, this
> feature allows a viewer to link multiple tracefiles belonging to the
> same channel and stream. This is particularly useful when dealing with
> tracefile rotation because the viewers will now be able to compute the
> accurate number of discarded events.
> Julien
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Mathieu Desnoyers
EfficiOS Inc.

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