Messages in this thread | | | Date | Thu, 03 Jul 2008 14:51:56 -0400 | From | Masami Hiramatsu <> | Subject | Re: [RFC PATCH] Kernel Tracepoints |
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Hi Mathieu,
Mathieu Desnoyers wrote: > * Masami Hiramatsu (mhiramat@redhat.com) wrote: >> 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? >> > > Yes, it is separate. This is insured by the fact that markers and > tracepoints are declared in different sections. Therefore, even if they > have the same "name", they won't be used by each other.
I reviewed both marker and tracepoint deeply in these days, and recognized what you said. Actually, markers and tracepoint would better have separate sections.
[...] >>>> - 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? >> > > When I originally designed the markers, I tried to make sure there was > absolutely no code duplication until I discovered that trying to read a > huge amount of nested macros is just a pain starting from a certain > level. If we only save a few duplicated lines but end up tying up > markers and tracepoints, I am far from certain that it will make the > code more readable.
After reviewing, I knew it is hard to implement markers on tracepoint. maybe, I need to find another way or maintenance both codes.
> I'll post a tracepoint version with the modifications you proposed (it's > now placed earlier in the patchset), except the merge with markers.
I see, if it is acceptable for upstream developers, I have no problem.
Thank you,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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