Re: [PATCH 1/9] perf/core: Add PERF_RECORD_CGROUP event

[Peter Zijlstra]

On Fri, Dec 20, 2019 at 01:32:45PM +0900, Namhyung Kim wrote:
> To support cgroup tracking, add CGROUP event to save a link between
> cgroup path and inode number.  The attr.cgroup bit was also added to
> enable cgroup tracking from userspace.
> 
> This event will be generated when a new cgroup becomes active.
> Userspace might need to synthesize those events for existing cgroups.
> 
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Li Zefan <lizefan@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>

TJ, is this the right thing to do? ISTR you had concerns on this topic
on the past.

> ---
>  include/uapi/linux/perf_event.h |  14 +++-
>  kernel/events/core.c            | 112 ++++++++++++++++++++++++++++++++
>  2 files changed, 125 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 377d794d3105..7bae2d3380a6 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -377,7 +377,8 @@ struct perf_event_attr {
>  				ksymbol        :  1, /* include ksymbol events */
>  				bpf_event      :  1, /* include bpf events */
>  				aux_output     :  1, /* generate AUX records instead of events */
> -				__reserved_1   : 32;
> +				cgroup         :  1, /* include cgroup events */
> +				__reserved_1   : 31;
>  
>  	union {
>  		__u32		wakeup_events;	  /* wakeup every n events */
> @@ -1006,6 +1007,17 @@ enum perf_event_type {
>  	 */
>  	PERF_RECORD_BPF_EVENT			= 18,
>  
> +	/*
> +	 * struct {
> +	 *	struct perf_event_header	header;
> +	 *	u64				id;
> +	 *	u64				path_len;

You can leave out path_len (also u64 for a length field is silly).

> +	 *	char				path[];
> +	 *	struct sample_id		sample_id;
> +	 * };
> +	 */
> +	PERF_RECORD_CGROUP			= 19,