On Wed, 2007-04-11 at 15:21 -0400, Mathieu Desnoyers wrote: > * Andrew Morton ([EMAIL PROTECTED]) wrote: > > On Wed, 11 Apr 2007 13:51:11 -0400 > > Mathieu Desnoyers <[EMAIL PROTECTED]> wrote: > > > > > > What's this marker stuff about? > > > > > > > > > > Hi Russel, > > > > > > Here is an overview : > > > > I am told that the systemtap developers plan to (or are) using this > > infrastructure. > > > > Quoting Frank Ch. Eigler, from the SystemTAP team : > > "The LTTng user-space programs use it today. Systemtap used to support > the earlier marker prototype and will be rapidly ported over to this > new API upon acceptance." > > > > If correct: what is their reason for preferring it over kprobes? > > > > I will let them answer on this one.. >
I'll take a shot at this one. First of all, kprobes remains a vital foundation for SystemTap. But markers are attactive as an alternate source of trace/debug info. Here's why: 1. Markers will live in the kernel and presumably be kept up to date by the maintainers of the enclosing code. We have a growing set of tapsets (probe libraries), each of which "knows" the source code for a certain area of the kernel. Whenever the underlying kernel code changes (e.g., a function or one of its args disappears or is renamed), there's a chance that the tapset will become invalid until we bring it back in sync with the kernel. As you can imagine, maintaining tapsets separate from the kernel source is a maintenance headache. Markers could mitigate this. 2. Because the kernel code is highly optimized, the kernel's dwarf info doesn't always accurately reflect which variables have which values on which lines (sometimes even upon entry to a function). A marker is a way to ensure that values of interest are available to SystemTap at marked points. 3. Sometimes the overhead of a kprobe probepoint is too much (either in terms of time or locking) for the particular hotspot we want to probe. Jim - 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/
