Re: oprofile: --kernel-range option of opcontrol utility not working as expected

[Maynard J. <may...@us...>]

B. N. Poornima wrote:

> Hello,
> We are noticing some problem with the opcontrol utility of oprofile in 
> the version 0.8.1 (and even the latest cvs code).
> If we pass the kernel range vma address to opcontrol using the 
> --kernel-range option, the profiling data that we get do not correspond 
> to the kernel-range addresses passed.

I've been looking into this some more and trying to understand the 
intended use of the --kernel-range option.  Firstly, it seems that in
your example, you have the start and end addresses swapped.  Maybe 
that's not the way you actually specified it when you ran oprofile, 
since I believe your output would have shown no vmlinux samples at all 
if your start value was greater than end value.

After looking at the code, it appears to me that the --kernel-range 
option is NOT intended as a filtering mechanism for recording samples 
that fall within the specified range -- but that seems to be your 
intended use.  Instead, I believe it is meant for the user to specify 
the actual VMA range in memory where the kernel resides.  For pLinux, 
this isn't necessary since the kernel is loaded into memory at the 
starting address specified as the starting VMA in the vmlinux image. 
Maybe --kernel-range is required for other flavors of Linux.

Does anyone on the list know the history of this option -- i.e., why 
does it exist?

Regards,
-Maynard
> For example,
> 
> opcontrol --start --kernel-range=43334f84,432a4c90 will give us the output:
> ********************************************************************************************
> vma	 samples   %       image name		    app name		     symbol name
> 000849d0 1         0.0851  vmlinux                  cat                      pipe_writev
> 000202e6 1         0.0851  vmlinux                  sshd                     sysc_do_restart
> 0000089a 1         0.0851  vmlinux                  vmlinux                  .lowcase
> 00031d34 1         0.0851  vmlinux                  vmlinux                  __do_softirq
> 0006a03c 1         0.0851  vmlinux                  vmlinux                  anon_vma_prepare
> 00062c84 1         0.0851  vmlinux                  vmlinux                  clear_page_tables
> 00064330 1         0.0851  vmlinux                  vmlinux                  do_wp_page
> 00199a00 1         0.0851  vmlinux                  vmlinux                  ip_rcv
> ***********************************************************************************************
> 
> This does not seem to change for different values of --kernel-range 
> passed.  Maynard P. Johnson (cced in the mail)/ /has tried to use the 
> latest cvs version, but still could not get this work. Can someone throw 
> more light on if this is the right way to use the option, is this a bug 
> and if so, has it been fixed in any of the
> recent releases?
> 
> Regards,
> Poornima
> 
> 
> 
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