[PATCH 1/4] arm: provide a mechanism to reserve performance counters

[Will Deacon]

* Jamie Iles <jamie.iles at picochip.com> wrote:

> To add support for perf events and to allow the hardware
> counters to be shared with oprofile, we need a way to reserve
> access to the pmu (performance monitor unit).
>
> Signed-off-by: Jamie Iles <jamie.iles <at> picochip.com>
> ---
> arch/arm/include/asm/pmu.h |   54 ++++++++++++++++++++++++++++++++++++++++++++
> arch/arm/kernel/Makefile   |    1 +
> arch/arm/kernel/pmu.c      |   32 ++++++++++++++++++++++++++
> arch/arm/mm/Kconfig        |    4 +++
> 4 files changed, 91 insertions(+), 0 deletions(-)
> create mode 100644 arch/arm/include/asm/pmu.h
> create mode 100644 arch/arm/kernel/pmu.c

Hi Jamie,

I like the idea of having a separate file for reserving the PMU across subsystems.
I also think it would be neat to extend it to request the relevant IRQs (or at
least return the PMU IRQs) once you've got it reserved.

This way, there will be no need to duplicate the inevitable collection of machine 
#ifdefs across tools [such as oprofile and perf]. It would also ensure that you can't 
reserve the PMU if somebody else has claimed the IRQs [and similarly, you can't
release it without giving them up].

What do you think?

Will