Messages in this thread | | | Date | Wed, 13 Jul 2022 09:35:56 +0530 | Subject | Re: [PATCH V6] arm64: perf: Make exporting of pmu events configurable | From | Srinivasarao Pathipati <> |
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On 6/24/2022 5:48 PM, Will Deacon wrote: > 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
Hi Will ,
We think it may not work. Say for example pmu->reset is called which disables the exporting of events, and pmu->start not called. This would lead to missing of events.
How about enabling it in both reset and start functions? do you see any issue?
--Srinivas
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