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SubjectRe: [PATCH V6] arm64: perf: Make exporting of pmu events configurable
On Thu, Jun 09, 2022 at 06:29:49PM +0530, Srinivasarao Pathipati wrote:
> The PMU export bit (PMCR_EL0.X) is getting reset during pmu reset,
> Make it configurable using sysctls to enable/disable at runtime.
>
> Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>
> ---
> Changes since V5:
> - removed configuring with kernel parameters.
> Changes since V4:
> - Registering sysctls dynamically for only arm64 as suggested by Will
> - Not removed the code to configure with kernel parameters
> as the sysctl's kernel parameter(sysctl.kernel.export_pmu_events)
> is not working at early bootup. pmu_reset() getting called before
> sysctl's kernel parameter is set.
> Changes since V3:
> - export bit is now configurable with sysctl
> - enabling export bit on reset instead of retaining
>
> Changes since V2:
> Done below changes as per Will's comments
> - enabling pmcr_x now configurable with kernel parameters and
> by default it is disabled.
>
> Changes since V1:
> - Preserving only PMCR_X bit as per Robin Murphy's comment.
>
> ---
> Documentation/admin-guide/sysctl/kernel.rst | 11 +++++++++++
> arch/arm64/kernel/perf_event.c | 13 +++++++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index ddccd10..c2ecd84 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -267,6 +267,17 @@ domain names are in general different. For a detailed discussion
> see the ``hostname(1)`` man page.
>
>
> +export_pmu_events (arm64 only)
> +==============================
> +
> +Controls the PMU export bit (PMCR_EL0.X), which enables the exporting of
> +events over an IMPLEMENTATION DEFINED PMU event export bus to another device.
> +
> +0: disables exporting of events (default).
> +
> +1: enables exporting of events.
> +
> +
> firmware_config
> ===============
>
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index cb69ff1..a8c32a0 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -298,6 +298,7 @@ PMU_FORMAT_ATTR(long, "config1:0");
> PMU_FORMAT_ATTR(rdpmc, "config1:1");
>
> static int sysctl_perf_user_access __read_mostly;
> +static int sysctl_export_pmu_events __read_mostly;
>
> static inline bool armv8pmu_event_is_64bit(struct perf_event *event)
> {
> @@ -1047,6 +1048,9 @@ static void armv8pmu_reset(void *info)
> if (armv8pmu_has_long_event(cpu_pmu))
> pmcr |= ARMV8_PMU_PMCR_LP;
>
> + if (sysctl_export_pmu_events)
> + pmcr |= ARMV8_PMU_PMCR_X;

I think we need to do this in armv8pmu_start() rather than armv8pmu_reset(),
otherwise any changes to the sysctl at runtime won't take effect unless you
do something like re-online the CPU.

Will

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