Subject: LTT for 2.6.19
Newsgroups: gmane.linux.kernel
Date: 2007-01-12 00:48:15 GMT (2 years, 24 weeks, 6 days, 7 hours and 58 minutes ago)
Hi, I'd like to introduce oldstyle ltt patches and tools supporting kernel 2.6.19. Beside support for newer kernel, there are other changes within these patches and tools: - storing descriptions of custom events in flight recording mode outside subbuffers (not to be overwriten in circular buffers), - way of timestamping (no more time deltas), - removed procfs usage for control, - initial implementation of static kernel markers (currently just for LTT), which does not change original kernel sources at any time. Links: base - http://84.255.254.67/linux-2.6.19-ltt-base.patch markers - http://84.255.254.67/linux-2.6.19-ltt-markers.patch tools - http://84.255.254.67/ltt-0.9.6-pre8.tar.gz Remark: New shell script files setmarker, createmarker and recreatemarkers under scripts directory need to be set as executables manually after patching the kernel with LTT base patch. - about custom events: There was a problem of overwritting descriptions of new custom events in flight recording mode, since those descriptions were stored sequentialy as any other ltt events in circular subbuffers. If descriptions were overwritten, collected custom events coud not be recognised. By storing descriptions outside subbuffers (in reley_reserved area if configured), these descriptions are being dumped inside the first dummy subbuffer. This dummy subbuffer has always been created at trace dump time in flight recording mode anyway and is almost empty. -about timestamping: I wanted to simplify things by using any kind of monotonic time within the system, which does not overflow in the reasonable lifetime of the system (even for an embedded type of application, which could be required to run for years without reboot). do_gettimeofday has already been such clock and for less overhead timestamping the complete 64 bits of TSC were used converted into nanoseconds. Luckily both clocks return 64 bit values, so a union of both types has been used for all ltt events to store its timestamp. In TSC mode sched_clock() is called to convert TSC values into nsecs and to be open for other architectures with TSC compareable counters (e.g. TB in ppc) in their sched_clock() functions. - about static kernel markers: This is an idea which came out of long running debates (many thanks to all involvedabout problematic managing of static markers within kernel code. Here is a possible way of getting around the need for a subsystem maintainer to even know about them (meaning markers). Since this tool uses direct calls to store events from fixed trace points in kernel source, a way to define those direct calls without modifying original sources has been implemented. The solution is quite primitive and involves a patch tool, a set of marker files (slightly modified patch files), a few scripts and a minimal modification of the kernel build subsystem. How this works: If markers are not to be used (kernel config option), everything is being compiled as always. But if kernel config option requires ltt markers to be used, each .c and .S file is being checked on the fly during compilation for its marker file. When a marker file has been found a new source file is created using a patch tool through the setmarker script and this new file gets compiled. It is easy to create a new marker file using createmarker script after manual preparation of marked file or after the use of a partially correct marker from another kernel version for example. All markers can be regenerated via recreatemarkers script, when all marked files have been prepared. I find this solution very handy at moving ltt patch to new kernel mainly because the patch includes real minimum of modified files and all the rest are just new files. And than during the first compilation using markers, patch tool is very helpfull resolving all nonconflicting modifications of the original files in the newer kernel. This implementation is just ltt oriented, but it could be done or used as more general static kernel marker solution as well. tracing new year, Samo