Hello
we are currently integrating and enhancing the LTTng Trace Control
plugin for Eclipse, that was originally provided as prototype by
Polytechnique de Montreal. Once all implementations are finished, the
plugin will be made available at the Linuxtools project within the
Eclipse foundation. This plugin connects as a client to a LTTng agent in
order to control the tracing of kernel or user space applications using
LTTng kernel or user space tracer. We have good progress but there are
some features (commands) missing in the LTTng agent which I think are
important for the user of the LTTng Trace Control. This email is to
point out this missing features and to get some feedback about my
suggestions.
My target node has the following versions installed:
- Ubuntu 10.10
- Instrumented kernel 2.6.35-24 installed from the PPA repository at
https://launchpad.net/~lttng/+archive/ppa
<https://launchpad.net/%7Elttng/+archive/ppa>
- manually upgraded UST 0.12
- manually upgraded lttng-agent from the git repository
(git.dorsal.polymtl.ca/git/lttng-agent.git), master branch of 23 March 2011
The LTTng agent provides commands to configure traces, markers or
channels. In some of the cases it's possible for the user to get that
information back form the agent (e.g. getActiveTraceInfo). However,
there are also many parameters which can't be retrieved. Generally
spoken, each parameter that can be set, there should be a command to get
that information back. See below for a list of missing commands and
other issues. I split the list between kernel and UST. The commands are
explained from the command line client point of view.
* Kernel
o There isn't any command to get the state of the tracing,
that means it's not possible to find out if an existing
trace is started or paused. As well as it's not possible to
retrieve the transport type (e.g. relay). It's possible to
retrieve all active traces (command: getActiveTraces) and
their configuration (getActiveTraceInfo), but the state and
transport is not available.
I propose to extend the command getActiveTraceInfo should be
extended to return the current state (started or paused).
Command: getActiveTraceInfo provider target trace
Output: {"target":"<target>","trace":"<trace>","destination":"<trace
path>","numThread":<# threads>,"flight_only":<flight
recorder>,"normal_only":<normal mode>,
"transport":<transport>, "is_started":<state>}
where:
<target>: the target name
<trace>: trace name
<trace path>: the trace path trace is local to the agent or
network when streaming
<# threads>: the number of threads
<flight recorder>: true for flight recorder mode else false
<normal mode>: true for normal mode else false
<transport> : the transport used
<is_started>: true if trace is started or false if trace is
paused
o There is a possibility to set parameters for channels, but
there is no way to retrieve this information. Here are the
set commands: setChannelEnable, setChannelOverride,
setChannelSubbufNum, setChannelSubbufSize and
setChannelTimer. There should be a command to retrieve that
information. To be consistent to the other get-commands I
propose the following command:
Command: getChannelInfo provider target trace channel
Output: {"target":"<target>","trace":"<trace>","channel":"<channel>",
"timer":<timer>, "is_enabled":<enable
state>,"is_override":<override state>,"subbuf_num":<#
subbuf>,"subbuf_size":<subbuf size>}
where:
<target>: the target name
<trace>: trace name
<channel>: the channel name
<timer>: channel timer in milliseconds
<enable state>: true if enabled
<override state>: true if override mode else false
<# subbuf>: number of sub buffers
<subbuf size>: size of sub buffer
* UST
o Currently it's not possible to create a UST trace using the
LTTng Trace control and LTTng agent. This needs to be
addressed and is currently looked at.
o For UST, there isn't a command to get the created traces for
a given target. Neither command getTraces nor
getActiveTraces is implemented as it is for kernel traces. I
understand that for UST there is always only 1 trace
possible per target (with name auto), but the user has to
have the possibility to retrieve the information from the
agent whether the trace has been created or not. I propose
to implement the commands getTraces and getActiveTraces.
o As for kernel traces, there should be the possibility to
retrieve the information about configured trace parameters.
I propose to implement getActiveTraceInfo which returns the
same information as for kernel traces (as proposed above)
o As for kernel traces, there should be the possibility to
retrieve the information about the configured channel
parameters. For UST, only the channel timer can be
configured and only one single timer is supported per
provider. I propose to use the getChannelInfo command as
proposed above for kernel traces (to be consistent).
Could you please give me some feedback about the above requested
enhancements of the LTTng agent? What are the future plans for the LTTng
agent? Is it possible to include these enhancements?
Best Regards
Bernd
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