* Dave Hansen ([EMAIL PROTECTED]) wrote: > On Wed, 2008-01-23 at 11:04 -0500, Mathieu Desnoyers wrote: > > Since memory management is not my speciality, I would like to know if > > there are some implementation details I should be aware of for my > > LTTng userspace tracing buffers. Here is what I want to do : > > Can you start with a little background by telling us what a userspace > tracing buffer _is_? Maybe a few requirements about what you need it to > do and why, as well? > > -- Dave >
Sure, Userspace tracing is : - A userspace process wants to record information to a circular ring buffer. This information has a timestamp. It should disrupt the timings minimally. The timestamps must be synchronized with the timestamps given to the kernel trace events so we can analyze all the information together. - When one subbuffer of the ring buffer is filled, the information is ready to be read by a "trace dumping" process and sent to disk or to the network. At this point, the traced process raises a flag that will be checked periodically by the OS to wake up the disk/network dumper daemon. (for future reference, I use the term "buffer writer" when I talk about the traced process and the term "buffer reader" when talking about the disk/network dumper daemon). There is more information in the email I sent to Frank Eigler. Please feel free to ask for more if I am not clear about specific points. A lot of the background information is already explained in the kernel tracing paper I presented at OLS2006, it might be a good start : http://ltt.polymtl.ca/papers/desnoyers-ols2006.pdf Another requirement I am trying to meet is protection of tracing buffers against corruption coming from other userspace process. K42 implemented their tracing buffers shared system-wide : with the OS too. The processes have full access to the kernel buffers and can therefore corrupt the whole system's trace. This is something I would like not to allow. Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
