Messages in this thread | | | Date | Tue, 11 Oct 2022 14:57:28 +0530 | Subject | Re: [PATCH V3 7/7] arm64/perf: Enable branch stack sampling | From | Anshuman Khandual <> |
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On 10/10/22 21:18, Suzuki K Poulose wrote: > On 10/10/2022 14:55, James Clark wrote: >> >> >> On 29/09/2022 08:58, Anshuman Khandual wrote: >>> Now that all the required pieces are already in place, just enable the perf >>> branch stack sampling support on arm64 platform, by removing the gate which >>> blocks it in armpmu_event_init(). >>> >>> Cc: Mark Rutland <mark.rutland@arm.com> >>> Cc: Will Deacon <will@kernel.org> >>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>> Cc: linux-kernel@vger.kernel.org >>> Cc: linux-arm-kernel@lists.infradead.org >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >>> --- >>> drivers/perf/arm_pmu.c | 32 +++++++++++++++++++++++++++++--- >>> 1 file changed, 29 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c >>> index 93b36933124f..2a9b988b53c2 100644 >>> --- a/drivers/perf/arm_pmu.c >>> +++ b/drivers/perf/arm_pmu.c >>> @@ -537,9 +537,35 @@ static int armpmu_event_init(struct perf_event *event) >>> !cpumask_test_cpu(event->cpu, &armpmu->supported_cpus)) >>> return -ENOENT; >>> - /* does not support taken branch sampling */ >>> - if (has_branch_stack(event)) >>> - return -EOPNOTSUPP; >>> + if (has_branch_stack(event)) { >>> + /* >>> + * BRBE support is absent. Select CONFIG_ARM_BRBE_PMU >>> + * in the config, before branch stack sampling events >>> + * can be requested. >>> + */ >>> + if (!IS_ENABLED(CONFIG_ARM_BRBE_PMU)) { >>> + pr_warn_once("BRBE is disabled, select CONFIG_ARM_BRBE_PMU\n"); >>> + return -EOPNOTSUPP; >>> + } >>> + >>> + if (event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_KERNEL) { >>> + if (!perfmon_capable()) { >> >> I'm still getting different behaviour compared to x86 when using >> perf_event_paranoid because of this perfmon_capable() call here. > > Given the generic events framework already checks this for any > privileged branch samples (i.e., for both KERNEL and HV), the > individual drivers must not add additional restrictions.
Okay, will drop perfmon_capable() check here along with the warning.
> >> >>> + pr_warn_once("does not have permission for kernel branch filter\n"); >> >> Also I was under the impression that this should be more like a >> KERN_INFO loglevel rather than a KERN_WARNING. It's more like expected >> behavior rather than unexpected behavior and as far as I know anyone who >> sees something in dmesg might think something has gone wrong and try to >> follow it up. It is quite a useful message but I remember getting a >> review like this before and it made sense to me. > > +1
Sure, will change remaining pr_warn_once() prints as pr_info() instead.
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