Re: [PATCH v10 2/5] perf: Add a counter for number of user access events in context

From: Mark Rutland
Date: Wed Oct 13 2021 - 13:26:44 EST


On Tue, Sep 14, 2021 at 03:47:57PM -0500, Rob Herring wrote:
> For controlling user space counter access, we need to know if any event
> in a context (currently scheduled or not) is using user space counters.
> Walking the context's list of events would be slow, so add a counter
> to track this.
>
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> ---
> v10:
> - Re-added.
> - Maintain the count in the perf core
> v9:
> - Dropped
> v8:
> - new patch
> ---
> include/linux/perf_event.h | 1 +
> kernel/events/core.c | 4 ++++
> 2 files changed, 5 insertions(+)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 12debf008d39..4f82a4d47139 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -821,6 +821,7 @@ struct perf_event_context {
>
> int nr_events;
> int nr_active;
> + int nr_user;
> int is_active;
> int nr_stat;
> int nr_freq;
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 744e8726c5b2..01290d150da3 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1808,6 +1808,8 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
>
> list_add_rcu(&event->event_entry, &ctx->event_list);
> ctx->nr_events++;
> + if (event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT)
> + ctx->nr_user++;
> if (event->attr.inherit_stat)
> ctx->nr_stat++;
>
> @@ -1999,6 +2001,8 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
> event->attach_state &= ~PERF_ATTACH_CONTEXT;
>
> ctx->nr_events--;
> + if (event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT)
> + ctx->nr_user--;
> if (event->attr.inherit_stat)
> ctx->nr_stat--;
>
> --
> 2.30.2
>