Hi Stefan, Thanks for the feedback! A few comments:
----- Original message ----- > Here is feedback from adding UST tracing to QEMU/KVM. Hopefully this > will be useful to developers and maybe I can learn a more about LTTng > UST from discussing hurdles I encountered. > > The architecture of UST looks good: pure userspace tracing support, > tracepoints can be enumerated, enabled, and disabled at runtime. The > manual at http://lttng.org/files/ust/manual/ust.html is a nice > quickstart although I suspect it only scratches the surface. If there are specific subjects in mind you feel would benefit from being covered in more depth in the manual, please let me know. > > One note about the manual: the TP_PROTO() versus TPPROTO() change was > confusing. Perhaps a note can be added to the manual that ust.git > uses TP_PROTO() but libust 0.4 uses TPPROTO()? This reflects an API change in the kernel. But you are right, this is confusing. I will do a 0.5 release next week, which will obsolete 0.4 and sync the manual. > > When running the instrumented binary, the listener thread outputs > noisy error messages: > libust[28133/28134]: Error: poll: Interrupted system call (in > multipoll_poll() at ../libustcomm/multipoll.c:84) > libust[28133/28134]: Error: error in multipoll_poll (in > listener_main() at tracectl.c:1015) > > Strace shows: > poll([{fd=3, events=POLLIN}], 1, -1) = ? ERESTART_RESTARTBLOCK (To > be restarted) > restart_syscall(<... resuming interrupted call ...>) = ? > ERESTART_RESTARTBLOCK (To be restarted) Hmmm. Do you have any pointers to documentation about this return code? I suspect userspace should never see it. Could it be a kernel bug? > > Finally, I had to add #undefs to get QEMU to build after including UST > headers. Unfortunately the UST headers include headers that pollute > the (macro) namespace. > From examining the patch, I expect you are referring to mutex_lock and _unlock. I just did a commit to fix this. > Any thoughts on these issues? > > My patch enabling UST sent to the QEMU mailing list: > http://www.mail-archive.com/[email protected]/msg34830.html Thanks! Pierre-Marc _______________________________________________ ltt-dev mailing list [email protected] http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
