Re: [PATCH v2 0/5] arm64: Enable access to pmu registers by user-space

[Raphael Gault <raphael.gault@arm.com>]

Hi,

Any further comments on this patchset ?

Cheers,

On 7/5/19 9:55 AM, Raphael Gault wrote:
> The perf user-space tool relies on the PMU to monitor events. It offers an
> abstraction layer over the hardware counters since the underlying
> implementation is cpu-dependent. We want to allow userspace tools to have
> access to the registers storing the hardware counters' values directly.
> This targets specifically self-monitoring tasks in order to reduce the
> overhead by directly accessing the registers without having to go
> through the kernel.
> In order to do this we need to setup the pmu so that it exposes its registers
> to userspace access.
> 
> The first patch add a test to the perf tool so that we can test that the
> access to the registers works correctly from userspace.
> 
> The second patch add a capability in the arm64 cpufeatures framework in
> order to detect when we are running on a heterogeneous system.
> 
> The third patch focuses on the armv8 pmuv3 PMU support and makes sure that
> the access to the pmu registers is enable and that the userspace have
> access to the relevent information in order to use them.
> 
> The fourth patch put in place callbacks to enable access to the hardware
> counters from userspace when a compatible event is opened using the perf
> API.
> 
> The fifth patch adds a short documentation about PMU counters direct
> access from userspace.
> 
> **Changes since v1**
> 
> * Rebased on linux-next/master
> * Do not include RSEQs materials (test and utilities) since we want to
>    enable direct access to counters only on homogeneous systems.
> * Do not include the hook defitinions for the same reason as above.
> * Add a cpu feature/capability to detect heterogeneous systems.
> 
> Raphael Gault (5):
>    perf: arm64: Add test to check userspace access to hardware counters.
>    arm64: cpufeature: Add feature to detect heterogeneous systems
>    arm64: pmu: Add function implementation to update event index in
>      userpage.
>    arm64: perf: Enable pmu counter direct access for perf event on armv8
>    Documentation: arm64: Document PMU counters access from userspace
> 
>   .../arm64/pmu_counter_user_access.txt         |  42 +++
>   arch/arm64/include/asm/cpucaps.h              |   3 +-
>   arch/arm64/include/asm/mmu.h                  |   6 +
>   arch/arm64/include/asm/mmu_context.h          |   2 +
>   arch/arm64/include/asm/perf_event.h           |  14 +
>   arch/arm64/kernel/cpufeature.c                |  20 ++
>   arch/arm64/kernel/perf_event.c                |  23 ++
>   drivers/perf/arm_pmu.c                        |  38 +++
>   include/linux/perf/arm_pmu.h                  |   2 +
>   tools/perf/arch/arm64/include/arch-tests.h    |   6 +
>   tools/perf/arch/arm64/tests/Build             |   1 +
>   tools/perf/arch/arm64/tests/arch-tests.c      |   4 +
>   tools/perf/arch/arm64/tests/user-events.c     | 255 ++++++++++++++++++
>   13 files changed, 415 insertions(+), 1 deletion(-)
>   create mode 100644 Documentation/arm64/pmu_counter_user_access.txt
>   create mode 100644 tools/perf/arch/arm64/tests/user-events.c
> 

-- 
Raphael Gault