Messages in this thread | | | Date | Mon, 10 Oct 2022 14:55:18 +0100 | Subject | Re: [PATCH V3 7/7] arm64/perf: Enable branch stack sampling | From | James Clark <> |
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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.
> + 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.
> + return -EPERM; > + } > + } > + > + /* > + * Branch stack sampling event can not be supported in > + * case either the required driver itself is absent or > + * BRBE buffer, is not supported. Besides checking for > + * the callback prevents a crash in case it's absent. > + */ > + if (!armpmu->brbe_supported || !armpmu->brbe_supported(event)) { > + pr_warn_once("BRBE is not supported\n"); > + return -EOPNOTSUPP; > + } > + } > > if (armpmu->map_event(event) == -ENOENT) > return -ENOENT;
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