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 <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Anshuman Khandual <[email protected]>
---
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()) {
+ pr_warn_once("does not have permission for kernel branch filter\n");
+ 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;
--
2.25.1
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 <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Anshuman Khandual <[email protected]>
> ---
> 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;
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 <[email protected]>
>> Cc: Will Deacon <[email protected]>
>> Cc: Catalin Marinas <[email protected]>
>> Cc: [email protected]
>> Cc: [email protected]
>> Signed-off-by: Anshuman Khandual <[email protected]>
>> ---
>> 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
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 <[email protected]>
>>> Cc: Will Deacon <[email protected]>
>>> Cc: Catalin Marinas <[email protected]>
>>> Cc: [email protected]
>>> Cc: [email protected]
>>> Signed-off-by: Anshuman Khandual <[email protected]>
>>> ---
>>> 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.