[lttng-dev] lttng create --output problem

[Ryan.Kyser at jci.com]

Mathieu:

Looks good! I went through my menuconfig and enabled all of these.

One suggestion -- change 'requied' to 'required' in the line 'Kernel 
config options requied'

Thank you,

Ryan Kyser




From:
Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
To:
Ryan.Kyser at jci.com
Cc:
lttng-dev at lists.lttng.org, David Goulet <dgoulet at efficios.com>
Date:
04/06/2012 12:31 PM
Subject:
Re: [lttng-dev] lttng create --output problem



* Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
> * Ryan.Kyser at jci.com (Ryan.Kyser at jci.com) wrote:
> > *** I'm resending this because I saw that mailman scrubbed my 
message.***
> > 
> > 
> > Mathieu:
> > 
> > I have provided the requested information below.
> > 
> > Also, I want to include some additional information which may (or may 
not) 
> > be part of the problem. When lttng-sessiond starts, I'm met with a 
> > modprobe error (see below). It looks as if this module is not being 
built 
> > at compile time because CONFIG_KVM is not enabled. However, if I go 
into 
> > the kernel menuconfig and search for KVM, no results are returned.
> 
> Normally lttng-modules should use the features that are there without
> complaining too much.
> 
> What I notice is that you don't have CONFIG_HAVE_SYSCALL_TRACEPOINTS
> enabled. So -k -a is enabling both tracepoints and syscalls, and given
> that syscall enabling returns ENOSYS, it prints this error and bails
> out.
> 
> The correct behavior would be to only fail of _both_ tracepoint and
> syscall instrumentation fail to enable.
> 
> Short term solution for you would be to enable
> CONFIG_HAVE_SYSCALL_TRACEPOINTS in your kernel.

FYI, here is the update. Feedback is welcome,

commit d0a5ff7d8479de94f1082055d1d940d660027fc8
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Fri Apr 6 12:32:22 2012 -0400

    Fix: document required and optional kernel config options in README
 
    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

diff --git a/README b/README
index abbfd27..ac0dc88 100644
--- a/README
+++ b/README
@@ -1,7 +1,7 @@
 LTTng 2.0 modules
 
 Mathieu Desnoyers
-February 8, 2012
+April 6, 2012
 
 LTTng 2.0 kernel modules build against a vanilla or distribution kernel, 
without
 need for additional patches. Other features:
@@ -48,9 +48,42 @@ LTTng 0.x patchset, but the lttng-modules 2.0 replace 
the lttng-modules
 0.x, so both tracers cannot be installed at the same time for a given
 kernel version.
 
-LTTng-modules depends on having kallsyms enabled in the kernel it is
-built against. Ideally, if you want to have system call tracing, the
-"Trace Syscalls" feature should be enabled too. 
+
+* Kernel config options requied
+
+CONFIG_KALLSYMS: required
+  * See wrapper/ files. This is necessary until the few required missing
+    symbols are exported to GPL modules from mainline.
+CONFIG_HIGH_RES_TIMERS: required
+  * Needed for LTTng 2.0 clock source.
+CONFIG_TRACEPOINTS: required
+    kernel tracepoint instrumentation
+    * Enabled as side-effect of any of the perf/ftrace/blktrace
+      instrumentation features.
+
+
+* Kernel config options supported (optional)
+
+The following kernel configuration options will affect the features
+available from LTTng:
+
+
+CONFIG_HAVE_SYSCALL_TRACEPOINTS:
+            system call tracing
+               lttng enable-event -k --syscall
+               lttng enable-event -k -a
+CONFIG_PERF_EVENTS:
+            performance counters
+               lttng add-context -t perf:*
+CONFIG_EVENT_TRACING:
+            needed to allow block layer tracing
+CONFIG_KPROBES: 
+            Dynamic probe.
+               lttng enable-event -k --probe ...
+CONFIG_KRETPROBES:
+            Dynamic function entry/return probe.
+               lttng enable-event -k --function ...
+
 
 * Note about Perf PMU counters support
 

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