* Ingo Molnar ([email protected]) wrote:
>
> * Roman Zippel <[email protected]> wrote:
>
> the key point is that we want _zero_ "static tracepoints". Firstly,
> static tracepoints are fundamentally limited:
>
> - they can only be added at the source code level
>
> - modifying them requires a reboot which is not practical in a
> production environment
Not for kernel modules : unload/load is enough.
> - there can only be a limited set of them, while many problems need
> finegrained tracepoints tailored to the problem at hand
Not true with the dynamic facility loading. LTTng can register new events upon
module load/unload.
>
> - conditional tracepoints are typically either nonexistent or very
> limited.
>
Maybe, but it can be useful to have static instrumentation available for those
limited conditional tracepoints.
> But besides the usability problems, the most important problem is that
> static tracepoints add a _constant maintainance overhead_ to the kernel.
> I'm talking from first hand experience: i wrote 'iotrace' (a static
> tracer) in 1996 and have maintained it for many years, and even today
> i'm maintaining a handful of tracepoints in the -rt kernel. I _dont_
> want static tracepoints in the mainline kernel.
>
If the trace points are modified with the code by the ones who make the
original code changes, it lessens the maintainance overhead. Furthermore, if
there is a major change in a code path that requires rethinking the trace
points, the person introducing the change has the best knowledge of what to do
with the trace point. I think that trace point maintainance should be left to
subsystem maintainers, not a centralised task done by distributions once in a
while.
Talking about experience, Karim has maintained the original LTT trace points,
which targeted key kernel event, for years without major trace points changes
between kernel versions. I think he already proved that maintainance of static
trace points in not an issue.
However, I restate that my position is that both static and dynamic
instrumentation of the kernel are a necessity and that a tracer core should be
usable by both.
Mathieu
OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg
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/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
