Re: [PATCH 00/10][RFC] tracing: Lowering the footprint of TRACE_EVENTs

[Mathieu Desnoyers <compudj@krystal.dyndns.org>]

* Steven Rostedt (rostedt@goodmis.org) wrote:
> This is an RFC patch set that also affects kprobes and perf.

Hi Steven,

> 
> At the Linux Collaboration Summit, I talked with Mathieu and others about
> lowering the footprint of trace events. I spent all of last week
> trying to get the size as small as I could.
> 
> Currently, each TRACE_EVENT() macro adds 1 - 5K per tracepoint. I got various
> results by adding a TRACE_EVENT() with the compiler, depending on
> config options that did not seem related. The new tracepoint I added
> would add between 1 and 5K, but I did not investigate enough to
> see what the true size was.

Adding only one might not give an accurate picture, as some sections can
be aligned on 4k boundaries. So if the added TRACE_EVENT() brings you to
the next 4k page, your added size is bumped of an extra 4k.

> 
> What was consistent, was the DEFINE_EVENT(). Currently, it adds
> a little over 700 bytes per DEFINE_EVENT().
> 
> This patch series does not seem to affect TRACE_EVENT() much (had
> the same various sizes), but consistently brings DEFINE_EVENT()s
> down from 700 bytes to 250 bytes per DEFINE_EVENT(). Since syscalls
> use one "class" and are equivalent to DEFINE_EVENT() this can
> be a significant savings.
> 
> With events and syscalls (82 events and 616 syscalls), before this
> patch series, the size of vmlinux was: 16161794, and afterward: 16058182.
> 
> That is 103,612 bytes in savings! (over 100K)
> 
> 
> Without tracing syscalls (82 events), it brought the size of vmlinux
> down from 1591046 to 15999394.

Probably a cut n paste error on the line above. Should read:

down from 16021465 to 15999394.

if you want the "22071 bytes in savings" to hold.

Will look over your patchset.

Thanks,

Mathieu

> 
> 22,071 bytes in savings.
> 
> This is just an RFC (for now), to get peoples opinions on the changes.
> It does a bit of rewriting of the CPP macros, just to warning you ;-)
> 
> -- Steve
> 
> The code can be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> tip/tracing/rfc-1
> 
> 
> Steven Rostedt (10):
>       tracing: Create class struct for events
>       tracing: Let tracepoints have data passed to tracepoint callbacks
>       tracing: Convert TRACE_EVENT() to use the DECLARE_TRACE_DATA()
>       tracing: Remove per event trace registering
>       tracing: Move fields from event to class structure
>       tracing: Move raw_init from events to class
>       tracing: Allow events to share their print functions
>       tracing: Move print functions into event class
>       tracing: Remove duplicate id information in event structure
>       tracing: Combine event filter_active and enable into single flags field
> 
> ----
>  include/linux/ftrace_event.h         |   71 +++++++++---
>  include/linux/syscalls.h             |   55 +++-------
>  include/linux/tracepoint.h           |  119 ++++++++++++++++---
>  include/trace/ftrace.h               |  215 ++++++++++------------------------
>  include/trace/syscall.h              |    9 +-
>  kernel/trace/blktrace.c              |   13 ++-
>  kernel/trace/kmemtrace.c             |   28 +++--
>  kernel/trace/trace.c                 |    9 +-
>  kernel/trace/trace.h                 |    5 +-
>  kernel/trace/trace_event_perf.c      |   17 ++-
>  kernel/trace/trace_events.c          |  126 +++++++++++++-------
>  kernel/trace/trace_events_filter.c   |   28 +++--
>  kernel/trace/trace_export.c          |   16 ++-
>  kernel/trace/trace_functions_graph.c |    2 +-
>  kernel/trace/trace_kprobe.c          |  104 ++++++++++-------
>  kernel/trace/trace_output.c          |  137 +++++++++++++++-------
>  kernel/trace/trace_output.h          |    2 +-
>  kernel/trace/trace_syscalls.c        |  105 +++++++++++++++--
>  kernel/tracepoint.c                  |   91 ++++++++-------
>  19 files changed, 700 insertions(+), 452 deletions(-)
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com