Re: [PATCH] Linux Kernel Markers

[Martin Bligh <mbligh@google.com>]

Mathieu Desnoyers wrote:
> * Vara Prasad (prasadav@us.ibm.com) wrote:
>
> > Martin Bligh wrote:
> >
> >
> > > [...]
> > > Depends what we're trying to fix. I was trying to fix two things:
> > >
> > > 1. Flexibility - kprobes seem unable to access all local variables etc
> > > easily, and go anywhere inside the function. Plus keeping low overhead
> > > for doing things like keeping counters in a function (see previous
> > > example I mentioned for counting pages in shrink_list).
> >
> > Using tools like systemtap on can consult DWARF information and put 
> > probes in the middle of the function and access local variables as well, 
> > that is not the real problem. The issue here is compiler doesn't seem to 
> > generate required DWARF information in some cases due to optimizations.  
> > The other related problem is when there exists debug information, the 
> > way to specify the breakpoint location is using line number which is not 
> > maintainable, having a marker solves this problem as well. Your proposal 
> > still doesn't solve the need for markers if i understood correctly.
>
> His implementation makes a heavy use of a marker mechanism : this is exactly
> what permits to create the instrumented objects from the same source code, but
> with different #defines.

I don't think it ties us to markers, though I think they're superior for
maintaintance, personally. It could equally well be an out of tree
normal flat patch with all the tracing in, which would make Andrew
happy, even if I think it sucks ;-)

M.
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