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SubjectRe: [PATCH v2 03/20] perf/core: add PERF_PMU_CAP_EXCLUDE for exclusion capable PMUs
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Hi Andrew,

On 26/11/2018 11:12, Andrew Murray wrote:
> Many PMU drivers do not have the capability to exclude counting events
> that occur in specific contexts such as idle, kernel, guest, etc. These
> drivers indicate this by returning an error in their event_init upon
> testing the events attribute flags. This approach is error prone and
> often inconsistent.
>
> Let's instead allow PMU drivers to advertise their ability to exclude
> based on context via a new capability: PERF_PMU_CAP_EXCLUDE. This
> allows the perf core to reject requests for exclusion events where
> there is no support in the PMU.
>
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
> include/linux/perf_event.h | 1 +
> kernel/events/core.c | 9 +++++++++
> 2 files changed, 10 insertions(+)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index b2e806f..69b3d65 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -244,6 +244,7 @@ struct perf_event;
> #define PERF_PMU_CAP_EXCLUSIVE 0x10
> #define PERF_PMU_CAP_ITRACE 0x20
> #define PERF_PMU_CAP_HETEROGENEOUS_CPUS 0x40
> +#define PERF_PMU_CAP_EXCLUDE 0x80
>
> /**
> * struct pmu - generic performance monitoring unit
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5a97f34..9afb33c 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9743,6 +9743,15 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
> if (ctx)
> perf_event_ctx_unlock(event->group_leader, ctx);
>
> + if (!ret) {
> + if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUDE) &&
> + event_has_any_exclude_flag(event)) {

Technically this is a bisection-breaker, since no driver has this
capability yet - ideally, this patch should come after all the ones
introducing it to the relevant drivers (with the removal of the
now-redundant code from the other drivers at the end).

Alternatively, since we already have several other negative
capabilities, unless there's a strong feeling against adding any more
then it might work out simpler to flip it to PERF_PMU_CAP_NO_EXCLUDE,
such that we only need to introduce the core check then directly replace
the open-coded event checks with the capability in the appropriate
drivers, and need not touch the exclusion-supporting ones at all.

Robin.

> + if (event->destroy)
> + event->destroy(event);
> + ret = -EINVAL;
> + }
> + }
> +
> if (ret)
> module_put(pmu->module);
>
>

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