Model-Specific Register

[William Cohen]

Lorenzo Cavallaro wrote:
> Hi,
> 
> On Tue, Oct 10, 2006 at 03:46:29PM -0400, Frank Ch. Eigler wrote:
> 
>>>   Beside that, I would like to measure (count) the number of branches (call,
>>>   jmp, jcc, loop) executed so far by a given process while it's executing in
>>>   user space. Do you think MSR (in particular) branch_retired register could
>>>   be useful for what I'm trying to do?
>>
>>Certainly.  Systemtap proper does not expose those registers yet, but
>>using e.g.  inline C code, it should be able to pull out such
>>information.
> 
> 
>    Cool. Any ideas (all the list, I mean :-)) on how to do it "from scratch"?
>    Never played with MSR at all.
> 
> 
>>>   Moreover, I would like to save this register (or a combo of
>>>   registers) into the process task_struct since I would like to
>>>   keep this counter accross processes' context switch [...]
>>
>>Check out the perfmon2 patches for the kernel.  Among other things, they
>>do this sort of context switch tracking.
> 
> 
>    Fine, thx! I'll check it out ASAP. :-)


There is some example code in systemtap bz#909 using perfmon2 to setup the 
registers using Perfmon2. You can also take a look at the patches for the 
runtime to figure out how to access the perfmon hw:

http://sources.redhat.com/bugzilla/show_bug.cgi?id=909


Perfmon2 has support to keep count of events on a per-thread basis. So you might 
not need to do much in the way of modification to accomplish what you want.

http://perfmon2.sourceforge.net/

-Will