Tracing Ceph With BlkKin

Ceph can use Blkin, a library created by Marios Kogias and others, which enables tracking a specific request from the time it enters the system at higher levels till it is finally served by RADOS.

In general, Blkin implements the Dapper tracing semantics in order to show the causal relationships between the different processing phases that an IO request may trigger. The goal is an end-to-end visualisation of the request’s route in the system, accompanied by information concerning latencies in each processing phase. Thanks to LTTng this can happen with a minimal overhead and in realtime. The LTTng traces can then be visualized with Twitter’s Zipkin.

Installing Blkin

You can install Markos Kogias’ upstream Blkin by hand.:

cd blkin/
make && make install

or build distribution packages using DistroReadyBlkin, which also comes with pkgconfig support. If you choose the latter, then you must generate the configure and make files first.:

cd blkin
autoreconf -i

Configuring Ceph with Blkin

If you built and installed Blkin by hand, rather than building and installing packages, then set these variables before configuring Ceph.:

export BLKIN_CFLAGS=-Iblkin/
export BLKIN_LIBS=-lzipkin-cpp

Blkin support in Ceph is disabled by default, so you may want to configure with something like:

./do_cmake -DWITH_BLKIN=ON

Config option for blkin must be set to true in ceph.conf to get traces from rbd through OSDC and OSD:

rbd_blkin_trace_all = true

Testing Blkin

It’s easy to test Ceph’s Blkin tracing. Let’s assume you don’t have Ceph already running, and you compiled Ceph with Blkin support but you didn’t install it. Then launch Ceph with the vstart.sh script in Ceph’s src directory so you can see the possible tracepoints.:

cd src
OSD=3 MON=3 RGW=1 ./vstart.sh -n
lttng list --userspace

You’ll see something like the following::

UST events:
-------------
PID: 8987 - Name: ./ceph-osd
      zipkin:timestamp (loglevel: TRACE_WARNING (4)) (type: tracepoint)
      zipkin:keyval_integer (loglevel: TRACE_WARNING (4)) (type: tracepoint)
      zipkin:keyval_string (loglevel: TRACE_WARNING (4)) (type: tracepoint)
      lttng_ust_tracelog:TRACE_DEBUG (loglevel: TRACE_DEBUG (14)) (type: tracepoint)

PID: 8407 - Name: ./ceph-mon
      zipkin:timestamp (loglevel: TRACE_WARNING (4)) (type: tracepoint)
      zipkin:keyval_integer (loglevel: TRACE_WARNING (4)) (type: tracepoint)
      zipkin:keyval_string (loglevel: TRACE_WARNING (4)) (type: tracepoint)
      lttng_ust_tracelog:TRACE_DEBUG (loglevel: TRACE_DEBUG (14)) (type: tracepoint)

...

Next, stop Ceph so that the tracepoints can be enabled.:

./stop.sh

Start up an LTTng session and enable the tracepoints.:

lttng create blkin-test
lttng enable-event --userspace zipkin:timestamp
lttng enable-event --userspace zipkin:keyval_integer
lttng enable-event --userspace zipkin:keyval_string
lttng start

Then start up Ceph again.:

OSD=3 MON=3 RGW=1 ./vstart.sh -n

You may want to check that ceph is up.:

./ceph status

Now put something in using rados, check that it made it, get it back, and remove it.:

./ceph osd pool create test-blkin 8
./rados put test-object-1 ./vstart.sh --pool=test-blkin
./rados -p test-blkin ls
./ceph osd map test-blkin test-object-1
./rados get test-object-1 ./vstart-copy.sh --pool=test-blkin
md5sum vstart*
./rados rm test-object-1 --pool=test-blkin

You could also use the example in examples/librados/ or rados bench.

Then stop the LTTng session and see what was collected.:

lttng stop
lttng view

You’ll see something like::

[15:33:08.884275486] (+0.000225472) ubuntu zipkin:timestamp: { cpu_id = 53 }, { trace_name = "op", service_name = "Objecter", port_no = 0, ip = "0.0.0.0", trace_id = 5485970765435202833, span_id = 5485970765435202833, parent_span_id = 0, event = "osd op reply" }
[15:33:08.884614135] (+0.000002839) ubuntu zipkin:keyval_integer: { cpu_id = 10 }, { trace_name = "", service_name = "Messenger", port_no = 6805, ip = "0.0.0.0", trace_id = 7381732770245808782, span_id = 7387710183742669839, parent_span_id = 1205040135881905799, key = "tid", val = 2 }
[15:33:08.884616431] (+0.000002296) ubuntu zipkin:keyval_string: { cpu_id = 10 }, { trace_name = "", service_name = "Messenger", port_no = 6805, ip = "0.0.0.0", trace_id = 7381732770245808782, span_id = 7387710183742669839, parent_span_id = 1205040135881905799, key = "entity type", val = "client" }

Install Zipkin

One of the points of using Blkin is so that you can look at the traces using Zipkin. Users should run Zipkin as a tracepoints collector and also a web service. The executable jar runs a collector on port 9410 and the web interface on port 9411

Download Zipkin Package:

git clone https://github.com/openzipkin/zipkin && cd zipkin
wget -O zipkin.jar 'https://search.maven.org/remote_content?g=io.zipkin.java&a=zipkin-server&v=LATEST&c=exec'
java -jar zipkin.jar

Show Ceph’s Blkin Traces in Zipkin-web

Download babeltrace-zipkin project. This project takes the traces generated with blkin and sends them to a Zipkin collector using scribe:

git clone https://github.com/vears91/babeltrace-zipkin
cd babeltrace-zipkin

Send lttng data to Zipkin:

python3 babeltrace_zipkin.py ${lttng-traces-dir}/${blkin-test}/ust/uid/0/64-bit/ -p ${zipkin-collector-port(9410 by default)} -s ${zipkin-collector-ip}

Example:

python3 babeltrace_zipkin.py ~/lttng-traces-dir/blkin-test-20150225-160222/ust/uid/0/64-bit/ -p 9410 -s 127.0.0.1

Check Ceph traces on webpage:

Browse http://${zipkin-collector-ip}:9411
Click "Find traces"