[Cbe-oss-dev] PS3 performance analysis - errors on loading cellperfctr module

[Carl Love]

I couldn't remember what the mode is called.  The systems that we worked
for the OProfile development on were all IBM CELL system.  The isolation
mode was not enabled.  However, from talking to the Hardware engineers
they said that in isolation mode the instruction to read the PC on the
SPUs would return 0 in isolation mode.  I never got a clear answer if
the instruction to read the PC on the PPU would also return 0 or not.
Hence my concern.  In addition to that, when you are in isolation mode,
there is hardware that is needed to get the SPU program counters which
is disabled.  

If the debug bus is disabled, you should still be able to access the
performance counter hardware control and data registers. The issue is
that you would not be able to route the performance counter event
signals to the performance counters is the bus is disabled.  These
signals all travel over the debug bus.  The only event that does not use
the debug bus is cycles.

I never had access to a machine with isolation mode enabled so I am not
sure exactly what will or will not work. Just wanted to give you a heads
up about the HW issues.  Don't want to see people spend a lot of work on
the hypervisor only to find the HW is disable.  So, just check on what
HW does work in isolation mode before investing too much effort.  

Good luck.

           Carl Love


 
On Wed, 2007-12-12 at 01:17 +0100, Arnd Bergmann wrote:
> On Wednesday 12 December 2007, Carl Love wrote:
> 
> > I do not believe you will get OProfile to work on the PS3.  It is my
> > understanding that the PS3 processor is shipped in with the hardware
> > security enabled.  The hardware security disables the reading of the
> > program counter.  It is part of the hardware security features to
> > prevent the reverse engineering of an application.  So, the fact that
> > the hypervisor support is not there really doesn't matter.  You will
> > need a PS3 system that does not have the hardware disabled.
> 
> You may be confusing this with the isolated mode of the SPUs. Linux
> on the PS3 does not use the isolated mode, so you can read the program
> counter just like you can on any other system.
> 
> The debug bus may also be disabled on the PS3, which means that you
> can't use the same method of accessing the performance counters that
> we use on the blade, but you should still be able to use the
> performance monitor registers by using hypercalls.
> 
> 	Arnd <><