Re: [RFC 2/2] perf: update userspace page info for software event

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jan 22, 2015 at 01:09:02PM -0800, Shaohua Li wrote:
> ---
>  kernel/events/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4edde3e..4221240 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5950,6 +5950,7 @@ static int perf_swevent_add(struct perf_event *event, int flags)
>  	}
>  
>  	hlist_add_head_rcu(&event->hlist_entry, head);
> +	perf_event_update_userpage(event);
>  
>  	return 0;
>  }
> @@ -6419,6 +6420,7 @@ static int cpu_clock_event_add(struct perf_event *event, int flags)
>  {
>  	if (flags & PERF_EF_START)
>  		cpu_clock_event_start(event, flags);
> +	perf_event_update_userpage(event);
>  
>  	return 0;
>  }
> @@ -6493,6 +6495,7 @@ static int task_clock_event_add(struct perf_event *event, int flags)
>  {
>  	if (flags & PERF_EF_START)
>  		task_clock_event_start(event, flags);
> +	perf_event_update_userpage(event);
>  
>  	return 0;
>  }

How about the one I sent; which adds it to {start,stop} instead of add?
{start,stop} is the right place to add them, although this add might be
sufficient for your use case.