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SubjectRe: [PATCH 00/10 final] tracing: Lowering the footprint of TRACE_EVENTs
On Wed, May 12, 2010 at 11:28:10AM -0400, Steven Rostedt wrote:
> [ Final final version! ]
> Ingo,
> This also affects kprobes and perf.
> At the Linux Collaboration Summit, I talked with Mathieu and others about
> lowering the footprint of trace events. I spent all of last two weeks
> 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.
> 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 618 syscalls), before this
> patch series, the size of vmlinux was: 6863829, and afterward: 6768675.
> That is 95,154 bytes in savings! (over 92K)
> Note: I did this series with disabling KERNEL_DEBUG and that made
> the effect of savings smaller. The original numbers with KERNEL_DEBUG
> options enabled was: orinal-16161794, new-16058182, savings-103612
> which was over 100K) This may still be true with KERNEL_DEBUG enabled
> but I only tried it this time with it disabled.
> But if I go by percentage, this series saves 1.38% where the
> KERNEL_DEBUG series only saved 0.64% of the total vmlinux image.
> Config for this run can be found here:
> Without tracing syscalls (82 events), it brought the size of vmlinux
> down from 6617121 to 659870.
> 18,421 bytes in savings.
> Note: Original numbers with KERNEL_DEBUG options enabled:
> original-1591046, new-15888394, savings-22071
> Final final changes:
> o Fixed trace_event.c self tests to use the probe field in the
> structure to determine if the event should be tested.
> (old regfunc no longer exists)
> o Fixed missing ';' in static struct in macro.
> o Fixed the trace register functions in net drop monitor to conform
> with the new API.
> Final changes:
> o Updated the change logs to reflect the sizes with KERNEL_DEBUG
> disabled.
> o Added Mathieu Desnoyers's Acked-by to the change logs.
> Changes in v3:
> o Ported to latest tip/tracing/core
> o Fixed typo in change log that a comment in LWN noticed:
> Wrote: 15999394 when it should have been 15888394.
> (Note: these numbers are from the original posting. I need to
> redo them again before posting officially).
> o Added Mathieu Desnoyers's check_trace patch that will check
> the callback to make sure it matches what DECLARE_TRACE() expects
> it.
> o Added the check_trace to the ftrace and perf callback probes.
> Note, kprobes and syscalls do not use the register tracepoint
> so they are not affected.
> o Moved the define of DECLARE_TRACE() and DECLARE_TRACE_NOARGS()
> out of the #ifdef CONFIG_TRACEPOINTS, since they were the same
> whether or not CONFIG_TRACEPOINTS was enabled. The internal
> __DECLARE_TRACE() changed.
> Changes in v2:
> o Ported to latest tip/tracing/core
> o Removed DECLARE_TRACE_DATA() and made DECLARE_TRACE() have
> the ability to pass a data parameter. This makes DECLARE_TRACE()
> not work with no args. A new DECLARE_TRACE_NOARGS() has been created
> that also allows data to be passed, but does is for tracepoint(void).
> o Made the callbacks be "proto, void *data" and typecast the data
> within the function.
> Please pull the latest tip/tracing/core tree, which can be found at:
> git://
> tip/tracing/core
> Mathieu Desnoyers (1):
> tracepoints: Add check trace callback type
> Steven Rostedt (9):
> tracing: Create class struct for events
> tracing: Let tracepoints have data passed to tracepoint callbacks
> 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

Acked-by: Frederic Weisbecker <>

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