Version 2.0-pre9

[lttng-modules.git] / README

diff --git a/README b/README
index 52bf44d9ee9bd4ad3f2c679742bbe1a17bc847dc..3bd0d153a7eacbe48e0b4dc25701a107e8153b06 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).
@@ -37,12 +37,19 @@ http://lttng.org/lttng2.0
 Please note that the LTTng-UST 2.0 (user-space tracing counterpart of LTTng 2.0)
 is still in active development and not released yet.
 
-So far, it has been tested on vanilla Linux kernels 2.6.38, 2.6.39 and 3.0-rc7
-(on x86 32/64-bit, and powerpc 32-bit at the moment). It should work fine with
-newer kernels and other architectures, but expect build issues with kernels
-older than 2.6.36. The clock source currently used is the standard gettimeofday
-(slower, less scalable and less precise than the LTTng 0.x clocks).  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
+So far, it has been tested on vanilla Linux kernels 2.6.38, 2.6.39 and 3.0 (on
+x86 32/64-bit, and powerpc 32-bit at the moment, build tested on ARM). It should
+work fine with newer kernels and other architectures, but expect build issues
+with kernels older than 2.6.36. The clock source currently used is the standard
+gettimeofday (slower, less scalable and less precise than the LTTng 0.x clocks).
+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.