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

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Date:   Wed, 13 Oct 2021 18:26:33 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Rob Herring <robh@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        honnappa.nagarahalli@....com, Zachary.Leaf@....com,
        Raphael Gault <raphael.gault@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 2/5] perf: Add a counter for number of user access
 events in context

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@...nel.org>

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

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
>