Messages in this thread | | | Date | Mon, 18 Sep 2006 01:03:10 -0400 | From | Mathieu Desnoyers <> | Subject | LTTng and SystemTAP (Everyone who is scared to read this huge thread, skip to here) |
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* Ingo Molnar (mingo@elte.hu) wrote: > so regarding the big picture we are largely on the same page in essence > i think - sub-issues non-withstanding :-) As long as LTT comes with a > facility that allows the painless moving of a static LTT markup to a > SystemTap script, that would come quite a bit closer to being acceptable > for upstream acceptance in my opinion. > > The curious bit is: why doesnt LTT integrate SystemTap yet? Is it the > performance aspect?
Yes, for our needs, the performance impact of SystemTAP is too high. We are totally open to integrate data coming from SystemTAP to our traces. Correct me if I am wrong, but I think their project does an extensive use of strings in the buffers. This is one, non compact, sub-optimal type, but it can do the job for low rate events. I also makes classification and identification of the information rather less straightforward. Plus, running a string format code in a critical code path does not give the kind of performance I am looking for.
> Some of the extensive hooking you do in LTT could be > aleviated to a great degree if you used dynamic probes. For example the > syscall entry hackery in LTT looks truly scary.
Yes, agreed. The last time I checked, I thought about moving this tracing code to the syscall_trace_entry/exit (used for security hooks and ptrace if I remember well). I just didn't have the time to do it yet.
> I cannot understand that > someone who does tracing doesnt see the fundamental strength of > SystemTap - i think that in part must have lead to my mistake of > assuming that you opposed SystemTap. >
Can you find a way to instrument it dynamically without the breakpoint cost ? System calls are a highly critical path both in a system and for tracing.
Mathieu
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