[PATCH 3/5] trace: Add LTTng Userspace Tracer backend

Stefan Hajnoczi
2010-05-22T21:08:37Z

This patch adds LTTng Userspace Tracer (UST) backend support. The UST
system requires no kernel support but libust and liburcu must be
installed.

$ ./configure --trace-backend ust
$ make

Start the UST daemon:
$ ustd &

List available tracepoints and enable some:
$ ustctl --list-markers $(pgrep qemu)
[...]
{PID: 5458, channel/marker: ust/paio_submit, state: 0, fmt: "acb %p
opaque %p sector_num %lu nb_sectors %lu type %lu" 0x4b32ba}
$ ustctl --enable-marker "ust/paio_submit" $(pgrep qemu)

Run the trace:
$ ustctl --create-trace $(pgrep qemu)
$ ustctl --start-trace $(pgrep qemu)
[...]
$ ustctl --stop-trace $(pgrep qemu)
$ ustctl --destroy-trace $(pgrep qemu)

Trace results can be viewed using lttv-gui.

More information about UST:
http://lttng.org/ust

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
I wrote this as part of trying out UST. Although UST is promising, the
usability is poor at the moment.

The dependencies include the lttv trace viewer which I had to build from source
(and it required a makefile tweak to build). Luckily libust, liburcu, and
ust-bin are packaged on my distro.

Error messages are periodically printed by the UST code when running QEMU. I
haven't investigated but this is may be due to signals interrupting UST's
thread in poll().

Finally, the UST header files include some userspace ported kernel
infrastructure and pollute the namespace. I had to add some #undefs to get
QEMU to build after including UST headers.

I don't see LTTng UST as a default option at the moment. Hopefully this will
change in the future.

configure | 5 +++-
tracetool | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index d599879..307dbcb 100755
--- a/configure
+++ b/configure
@@ -829,7 +829,7 @@ echo " --enable-docs enable documentation build"
echo " --disable-docs disable documentation build"
echo " --disable-vhost-net disable vhost-net acceleration support"
echo " --enable-vhost-net enable vhost-net acceleration support"
-echo " --trace-backend=B Trace backend nop simple"
+echo " --trace-backend=B Trace backend nop simple ust"
echo ""
echo "NOTE: The object files are built at the place where configure is launched"
exit 1
@@ -2302,6 +2302,9 @@ bsd)
esac

echo "TRACE_BACKEND=$trace_backend" >> $config_host_mak
+if test "$trace_backend" = "ust"; then
+ LIBS="-lust $LIBS"
+fi

tools=
if test `expr "$target_list" : ".*softmmu.*"` != 0 ; then
diff --git a/tracetool b/tracetool
index bcd163e..72beb20 100755
--- a/tracetool
+++ b/tracetool
@@ -3,12 +3,13 @@
usage()
{
cat >&2 <<EOF
-usage: $0 [--nop | --simple] [-h | -c | --py]
+usage: $0 [--nop | --simple | --ust] [-h | -c | --py]
Generate tracing code for a file on stdin.

Backends:
--nop Tracing disabled
--simple Simple built-in backend
+ --ust LTTng User Space Tracing backend

Output formats:
-h Generate .h file
@@ -220,6 +221,78 @@ linetopy_end_simple()
echo "}"
}

+linetoh_begin_ust()
+{
+ echo "#include <ust/tracepoint.h>"
+}
+
+linetoh_ust()
+{
+ local name args argnames
+ name=$(get_name "$1")
+ args=$(get_args "$1")
+ argnames=$(get_argnames "$1")
+
+ cat <<EOF
+DECLARE_TRACE(ust_$name, TPPROTO($args), TPARGS($argnames));
+#define trace_$name trace_ust_$name
+EOF
+}
+
+linetoh_end_ust()
+{
+ # Clean up after UST headers which pollute the namespace
+ cat <<EOF
+#undef mutex_lock
+#undef mutex_unlock
+EOF
+}
+
+linetoc_begin_ust()
+{
+ cat <<EOF
+#include <ust/marker.h>
+#include "trace.h"
+EOF
+}
+
+linetoc_ust()
+{
+ local name args argnames fmt
+ name=$(get_name "$1")
+ args=$(get_args "$1")
+ argnames=$(get_argnames "$1")
+ fmt=$(get_fmt "$1")
+
+ cat <<EOF
+DEFINE_TRACE(ust_$name);
+
+static void ust_${name}_probe($args)
+{
+ trace_mark(ust, $name, "$fmt", $argnames);
+}
+EOF
+
+ # Collect names for later
+ names="$names $name"
+}
+
+linetoc_end_ust()
+{
+ cat <<EOF
+static void __attribute__((constructor)) trace_init(void)
+{
+EOF
+
+ for name in $names; do
+ cat <<EOF
+ register_trace_ust_$name(ust_${name}_probe);
+EOF
+ done
+
+ echo "}"
+}
+
# Process stdin by calling begin, line, and end functions for the backend
convert()
{
@@ -267,7 +340,7 @@ tracetopy()

# Choose backend
case "$1" in
-"--nop" | "--simple") backend="${1#--}" ;;
+"--nop" | "--simple" | "--ust") backend="${1#--}" ;;
*) usage ;;
esac
shift
--
1.7.1