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

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