RFC Tracer Timestamping

Hi,

Starting with the bottom of my LTTng patchset
(git://git.kernel.org/pub/scm/linux/kernel/git/compudj/linux-2.6-lttng.git)
I post as RFC the timestamping infrastructure I have been using for a while in the tracer. It integrates get_cycles() standardization following David Miller's comments I did more recently.

It also deals with 32 -> 64 bits timestamp counter extension with a RCU-style algorithm, which is especially useful on MIPS and SuperH architectures.

There is also a TSC synchronization test within this patchset to detect unsynchronized TSCs. See comments in this specific patch to figure out the difference between the current x86 tsc_sync.c and the one I propose in this patch.

It also provides an architecture-agnostic fallback in case there is no timestamp counter available : basically, it's
(jiffies << 13) | atomically_incremented_counter (if there are more than 8192 events per jiffy, time will still be monotonic, but will increment faster than the actual system frequency).

Comments are welcome. Note that this is only the beginning of the patchset. I plan to submit the event ID allocation/portable event typing aimed at exporting the data to userspace and buffering mechanism as soon as I integrate a core version of the LTTV userspace tools to the kernel build tree. Other than that, I currently have a tracer which fulfills most of the requirements expressed earlier. I just fear that if I release only the kernel part without foolproof binary-to-ascii trace decoder within the kernel, people might be a bit reluctant to fetch a separate userspace package.

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