More 16 vs 24 bpp profiling

[Stefano Fedrigo]

Jordan Crouse wrote:
>> Unfortunately without a working callgraph it's not very clear to me what's
>> happening in amd_drv.  At 24bpp gp_wait_until_idle() takes twice the time...
> 
> What can we do to fix this?  I would really like to know who is calling
> gp_wait_until_idle().

The problem seems to be that, on the XO, oprofile can only use an event timer 
that doesn't allow accurate stack tracing.  The process stack is not accessible 
inside the interrupt used for sampling.
I hope there is some way to solve this issue because, in kernel code, call 
tracing works, provided the kernel is compiled with frame pointers.
I had not the time to look at this in depth, perhaps selecting a different
interrupt source, if possible, is enough to have callgraphs in userspace
code.