The following patches are a cleaned up version of the work Marios Kogias first posted in August. http://www.spinics.net/lists/ceph-devel/msg19890.html This patch is against HEAD as of March 2nd at 4:30pm Mountain. It can also be found at https://github.com/agshew/ceph/tree/wip-blkin-v5 Thanks to Josh Durgin for walking through the V4 patchset with me and helping with all of the issues described in the changelog below. And thanks to Sage for discussing the problems associated with the messenger_end trace event. Outstanding issues: I've seen OSD startup failures, which are probably due to the blkin patchset moving the call to global_init_daemonize() to earlier in ceph_osd.c:main(). Sage had already warned that moving OSD daemonize is not safe, so I attempted to not move it. Unfortunately, this leads to a segfault. Either blkin needs initialized sooner as Marios had done, or certain tracing calls needed to be made conditional on blkin's initialization. So, I then attempted to modify blkin's ZTracer::create_ZTraceEndpoint(), which valgrind pointed at, to only create the endpoint if blkin_init() had been called. But that patch resulted in bad health as reported by './ceph status': health HEALTH_WARN mds a,b,c are laggy ... For now, I've continued with Marios' original global_init_daemonize() move. After fixing the outstanding issues: 1. push a wip-blkin branch to github.com/ceph and take advantage of gitbuilder test/qa 2. submit a pull request 3. add Andreas' tracepoints https://github.com/ceph/ceph/pull/2877 using Blkin and investigate how easy it is to select the level of tracing detail Changes since V4: * removed messenger_end trace event In Pipe::reader(), when message is enqueued, it will be destroyed. Naive pointer checks don't work here. You can't depend on pointers being set to null on destruction. It may be possible to wrap trace event with m->get() and m->put() to keep it around, or put this trace event in dispatch paths, but just removing trace event for now in order to move forward. * removed mutex in aio_*_traced() methods A mutex was carried forward from Marios' original patch while rebasing when it should have been removed. * removed Message::trace_end_after_span Message::trace_end_after_span did not ever appear to be true, so it has been removed * added asserts for master trace and endpoint checks Tried to use asserts in more places, but they prevented execution. Tried to use douts and ldouts instead, but they didn't work. * added parens around macro pointer args parens make it safer to use pointers passed as arguments in a macro Changes since V2: * WITH_BLKIN added to makefile vars when necessary * added Blkin build instructions * added Zipkin build instructions * Blkin wrapper macros do not stringify args any longer. The macro wrappers will be more flexible/robust if they don't turn arguments into strings. * added missing blkin_trace_info struct prototype to librados.h * TrackedOp trace creation methods are virtual, implemented in OpRequest * avoid faults due to non-existent traces Check if osd_trace exists when creating a pg_trace, etc. Return true only if trace creation was successful. Use dout() if trace_osd, trace_pg, etc. fail, in order to ease debugging. * create trace_osd in ms_fast_dispatch Changes since V1: * split build changes into separate patch * conditional build support for blkin (default off) * blkin is not a Ceph repo submodule build and install packages from https://github.com/agshew/blkin.git Note: rpms don't support babeltrace plugins for use with Zipkin * removal of debugging in Message::init_trace_info() With this patchset 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 tracing semantics described in the Dapper paper http://static.googleusercontent.com/media/research.google.com/el/pubs/archive/36356.pdf in order to trace 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. In order to visualize the results Blkin was integrated with Twitter's Zipkin http://twitter.github.io/zipkin/ (which is a tracing system entirely based on Dapper). A short document describing how to test Blkin tracing in Ceph with Zipkin is in doc/dev/trace.rst -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
