[lttng-dev] Writing .tp files for lttng-gen-tp

[Philippe Proulx]

On Sat, Oct 18, 2014 at 5:16 PM, Boisvert, Sebastien <boisvert at anl.gov> wrote:
> Hi,
>
> Since all my thorium_message:* tracepoints have the same arguments and same fields,
> should I instead use one single tracepoint with an additional argument and field for
> the calling context ("actor_receive", "node_receive", and so on):

I was waiting for this question ;-).

I wouldn't recommend recording a string each time. At the very least, you
could use an integer identifier, which won't impact your app's performance
as much as copying a string for each event.

But, ultimately, I think the different names approach is the best. The TP name
is supposed to pinpoint a specific, static location in your source code, and
that's exactly what you're doing now. Plus, you would need to add a filter,
which is some interpreted bytecode executed when the event fires, whenever
you want to disable specific tracepoints, whereas LTTng is designed to
enable/disable TP easily using TP names.

Phil
>
>
> TRACEPOINT_EVENT(
>     thorium,
>     message_delivery_path,
>     TP_ARGS(
>         char *, context,
>         struct thorium_message *, message
>     ),
>     TP_FIELDS(
>         ctf_string(context, context)
>         ctf_integer(int, message_number, message->number)
>         ctf_integer(int, message_action, message->action)
>         ctf_integer(int, message_count, message->count)
>         ctf_integer(int, message_source_actor, message->source_actor)
>         ctf_integer(int, message_destination_actor, message->destination_actor)
>         ctf_integer(int, message_source_node, message->source_node)
>         ctf_integer(int, message_destination_node, message->destination_node)
>     )
> )
>
>
> I feel like this is better, but I don't know if this a good practice to do this with LTTng.
>
>> ________________________________________
>> From: Philippe Proulx [eeppeliteloop at gmail.com]
>> Sent: Saturday, October 18, 2014 12:58 PM
>> To: Boisvert, Sebastien
>> Cc: lttng-dev at lists.lttng.org
>> Subject: Re: [lttng-dev] Writing .tp files for lttng-gen-tp
>> On Sat, Oct 18, 2014 at 10:39 AM, Boisvert, Sebastien <boisvert at anl.gov> wrote:
>> >
>> > Hi,
>> >
>> > I changed the provider name to thorium_message.
>> >
>> > I also tried using a macro in the template file, but the define alone
>> > breaks things.
>> >
>> > Template file: https://github.com/sebhtml/biosal/blob/master/engine/thorium/tracepoints/lttng/message.tp (the macro is commented)
>> >
>> >
>> > Uncommenting the macro produces these warnings:
>> >
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> > Warning: different domain provided (int,thorium_message)
>> >
>> > And the linker fails.
>> Yes, sorry about that, I didn't look at the output.
>> lttng-gen-tp has some bugs. It parses everything using regexes, so I guess it
>> won't deal properly with custom C preprocessor stuff reusing
>> TRACEPOINT_EVENT() within a macro. For some reason, it detects `int` as
>> the tracepoint provider name ("domain" in lttng-gen-tp's jargon).
>> IMO your use case might already be too advanced for lttng-gen-tp, so I would
>> advise that you have a look at defining plain tracepoint providers without
>> using lttng-gen-tp: <http://lttng.org/docs/#doc-tracepoint-provider>. It
>> basically involves writing a proper template header. The hardest part
>> is defining
>> the tracepoints using TRACEPOINT_EVENT(), but you already did that.
>> So start with this (TP provider name fixed):
>> * message.h: <http://pastebin.com/yiqN0CEj>
>> * message.c: <http://pastebin.com/BmXiSCbd>
>> Build it like this:
>> gcc -I../../../.. -I. -c message.c
>> and link the resulting message.o with your application as usual.
>> >
>> > > ________________________________________
>> > > From: Philippe Proulx [eeppeliteloop at gmail.com]
>> > > Sent: Friday, October 17, 2014 9:36 PM
>> > > To: Boisvert, Sebastien
>> > > Cc: lttng-dev at lists.lttng.org
>> > > Subject: Re: [lttng-dev] Writing .tp files for lttng-gen-tp
>> > > On Fri, Oct 17, 2014 at 5:39 PM, Boisvert, Sebastien <boisvert at anl.gov> wrote:
>> > > > Hi,
>> > > >
>> > > > I wrote a big .tp file to define numerous tracepoints that only differ in the event name.
>> > > > They all take the same arguments and they all dump the same fields.
>> > > >
>> > > >
>> > > > .tp file: https://github.com/sebhtml/biosal/blob/master/engine/thorium/tracepoints/lttng/message.tp
>> > > >
>> > > >
>> > > > Is there a more compact way of doing that ?
>> > > Yes; note that a template file is just part of an eventual C header
>> > > file, so C preprocessor
>> > > stuff is accepted. This should work:
>> > > #include <engine/thorium/message.h>
>> > > #define THORIUM_MSG_TP(name) \
>> > > TRACEPOINT_EVENT( \
>> > > message, \
>> > > name, \
>> > > TP_ARGS( \
>> > > struct thorium_message *, msg \
>> > > ), \
>> > > TP_FIELDS( \
>> > > ctf_integer(int, message_number, msg->number) \
>> > > ctf_integer(int, message_action, msg->action) \
>> > > ctf_integer(int, message_count, msg->count) \
>> > > ctf_integer(int, message_source_actor, msg->source_actor) \
>> > > ctf_integer(int, message_destination_actor,
>> > > msg->destination_actor) \
>> > > ctf_integer(int, message_source_node, msg->source_node) \
>> > > ctf_integer(int, message_destination_node,
>> > > msg->destination_node) \
>> > > ) \
>> > > )
>> > > THORIUM_MSG_TP(actor_send)
>> > > THORIUM_MSG_TP(node_send)
>> > > THORIUM_MSG_TP(worker_send)
>> > > THORIUM_MSG_TP(worker_receive)
>> > > THORIUM_MSG_TP(worker_send_mailbox)
>> > > THORIUM_MSG_TP(worker_send_schedule)
>> > > THORIUM_MSG_TP(worker_pool_enqueue)
>> > > THORIUM_MSG_TP(worker_pool_dequeue)
>> > > THORIUM_MSG_TP(worker_enqueue_message)
>> > > THORIUM_MSG_TP(actor_receive)
>> > > THORIUM_MSG_TP(worker_dequeue_message)
>> > > THORIUM_MSG_TP(node_send_system)
>> > > THORIUM_MSG_TP(node_receive)
>> > > THORIUM_MSG_TP(node_receive_message)
>> > > THORIUM_MSG_TP(node_send_dispatch)
>> > > THORIUM_MSG_TP(node_dispatch_message)
>> > > THORIUM_MSG_TP(transport_send)
>> > > THORIUM_MSG_TP(transport_receive)
>> > > Please write back if it does not.
>> > > BTW, I would suggest that your tracepoint provider name (currently `message`) be
>> > > more specific as to what your application really is, e.g., `thorium_msg`.
>> > > Phil
>> > > >
>> > > >
>> > > >                 Sébastien
>> > > >
>> > > >
>> > > > _______________________________________________
>> > > > lttng-dev mailing list
>> > > > lttng-dev at lists.lttng.org
>> > > > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev