Messages in this thread | | | Date | Mon, 10 Oct 2022 16:48:32 +0100 | Subject | Re: [PATCH V3 7/7] arm64/perf: Enable branch stack sampling | From | Suzuki K Poulose <> |
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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.
> >> + 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
Suzuki
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