From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefanha@gmail.com (Stefan Hajnoczi) Date: Thu, 27 May 2010 06:21:27 +0100 Subject: [ltt-dev] UST use case: Tracing QEMU/KVM In-Reply-To: <4BFDA4BE.4020400@polymtl.ca> References: <1274673453.6759.5.camel@Nokia-N900-42-11> <4BFDA4BE.4020400@polymtl.ca> Message-ID: On Wed, May 26, 2010 at 11:46 PM, Pierre-Marc Fournier wrote: >> For large programs or programs that closely manage resources, a >> documented list of resources that libust uses would be useful. ?This >> information can be used to understand whether libust might interfere >> with the program being traced. ?For example, will heap allocations be >> made after startup? ?Will file descriptors be held open? ?The listener >> thread? > > Currently, ust is designed to be transparent to the running process in most > cases. However, if your program makes very unusual assumptions about the > usage of some resources, this could result in a conflict. > > - Yes, heap allocations can be made after startup. > - Sockets will definitely be kept open by the listener thread. > - Currently, I don't think any file descriptors are kept open, but it could > be the case in the future. > - SystemV shared memory segments are mapped in the address space. > - A listener thread is always started to wait for connections from ustctl or > ustd. > > If you feel it would be important to avoid some of these things, please let > me know. Thanks for explaining, sounds fine to me. If you want to add this as an appendix to the documentation I think it is useful information for an application developer who wants to integrate UST support. >> I don't understand the --create-trace, --alloc-trace, --destroy-trace, >> and subbuf concepts that ustctl exposes. ?Perhaps these are documented >> in kernel LTTng and I haven't read that. > > Normally you should not need to go to LTTng kernel tracer documentation to > understand. > > I just pushed an updated manpage for ustctl in the git which clarifies these > concepts. If you think things could be even clearer, let me know. Great thanks, will check out the documentation. Stefan