Mass rename: ltt_*/ltt-* to LTTNG_*/LTTNG-*

[lttng-modules.git] / README

diff --git a/README b/README
index 583d0e024864d2e37fd22a86d847ec955539b1d7..f4e3368cec50bad0d3f88465d565193617d6abf5 100644 (file)
--- a/README
+++ b/README
@@ -9,7 +9,7 @@ need for additional patches. Other features:
 - Produces CTF (Common Trace Format) natively,
   (http://www.efficios.com/ctf)
 - Tracepoints, Function tracer, CPU Performance Monitoring Unit (PMU)
-  counters and kprobes support,
+  counters, kprobes, and kretprobes support,
 - Integrated interface for both kernel and userspace tracing,
 - Have the ability to attach "context" information to events in the
   trace (e.g. any PMU counter, pid, ppid, tid, comm name, etc).
@@ -22,12 +22,14 @@ access to your full kernel source tree), and use:
 
 % make
 # make modules_install
+# depmod -a
 
 If you need to specify the target directory to the kernel you want to build
 against, use:
 
 % KERNELDIR=path_to_kernel_dir make
 # KERNELDIR=path_to_kernel_dir make modules_install
+# depmod -a kernel_version
 
 Use lttng-tools to control the tracer. LTTng tools should automatically load
 the kernel modules when needed. Use Babeltrace to print traces as a
@@ -46,3 +48,10 @@ Support for LTTng 0.x clocks will be added back soon into LTTng 2.0.  Please
 note that lttng-modules 2.0 can build on a Linux kernel patched with the 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.
+
+* Note about Perf PMU counters support
+
+Each PMU counter has its zero value set when it is attached to a context with
+add-context. Therefore, it is normal that the same counters attached to both the
+stream context and event context show different values for a given event; what
+matters is that they increment at the same rate.