Re: [RFC PATCH] Kernel Tracepoints

[Masami Hiramatsu <mhiramat@redhat.com>]

Hi Mathieu,

Mathieu Desnoyers wrote:
> * Masami Hiramatsu (mhiramat@redhat.com) wrote:
>> Mathieu Desnoyers wrote:
>>> * Masami Hiramatsu (mhiramat@redhat.com) wrote:
>>>  >
>>>>> Implementation of kernel tracepoints. Inspired from the Linux Kernel Markers.
>>>> What would you think redesigning markers on tracepoints? because most of the
>>>> logic (scaning sections, multiple probe and activation) seems very similar
>>>> to markers.
>>>>
>>> We could, although markers, because they use var args, allow to put the
>>> iteration on the multi probe array out-of-line. Tracepoints cannot
>>> afford this and the iteration must be done at the initial call-site.
>>>
>>> From what I see in your proposal, it's mostly to extract the if() call()
>>> code from the inner __trace_mark() macro and to put it in a separate
>>> macro, am I correct ? This would make the macro more readable.
>> Sure, I think marker and tracepoint can share below functions;
>> - definition of static local variables in specific sections
> 
> Given that we could want to keep activation of tracepoints and markers
> separate (so they don't share the same namespace), declaring the static
> variables in separated sections seems to make sense to me.

Sorry, I'm not sure what is "separate activation".
As far as I can see, both tracepoints and markers are activated
when its probe handlers are registered on each tracepoint/marker.
Aren't it separated?

I did not mean integrating registering interfaces, but
I think that they can share base(internal) functions.
for example, both of them has XXX_update_range/_module_XXX_update etc.

IMHO, current code is not so good for maintenance. there are
many code duplications (ex. kernel/module.c, I think
that both of them (and imv too?) can share the code for
handling its section and iterating entries). I'm not sure those
duplications are acceptable.

>> - probe activation code (if() call())
>> - multi probe handling
> 
> Hrm, the thing here is that because markers allow to do the iteration on
> the multiple probe callbacks within an internal wrapper (instead of
> doing it on-site as in the tracepoints), it allows to do some further
> optimizations (less memory allocation and less pointer dereference in
> the single probe case, not having to prepare the va_args in the
> MARK_NOARGS case) which are only done because it does not have to add
> code to the instrumentation site. However, tracepoints cannot have such
> "generic" wrapper and we have to do the iteration on callbacks in the
> code added to the instrumented object. Therefore, I keep it as small as
> possible in terms of bytes of instructions.

OK, I see. So, __tracepoint_block() macro can specify handler function.
what would you think about it?

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com