linux-kernel - Re: [PATCH 2/9] perf/core: Add PERF_SAMPLE

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Date:   Fri, 20 Dec 2019 10:36:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Stephane Eranian <eranian@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/9] perf/core: Add PERF_SAMPLE_CGROUP feature

On Fri, Dec 20, 2019 at 01:32:46PM +0900, Namhyung Kim wrote:
> The PERF_SAMPLE_CGROUP bit is to save (perf_event) cgroup information
> in the sample.  It will add a 64-bit id to identify current cgroup and
> it's the file handle in the cgroup file system.  Userspace should use
> this information with PERF_RECORD_CGROUP event to match which cgroup
> it belongs.
> 
> I put it before PERF_SAMPLE_AUX for simplicity since it just needs a
> 64-bit word.  But if we want bigger samples, I can work on that
> direction too.
> 
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---

> @@ -6895,6 +6901,18 @@ void perf_prepare_sample(struct perf_event_header *header,
>  	if (sample_type & PERF_SAMPLE_PHYS_ADDR)
>  		data->phys_addr = perf_virt_to_phys(data->addr);
>  
> +	if (sample_type & PERF_SAMPLE_CGROUP) {
> +		u64 cgrp_id = 0;
> +#ifdef CONFIG_CGROUP_PERF
> +		struct cgroup *cgrp;
> +
> +		/* protected by RCU */
> +		cgrp = task_css_check(current, perf_event_cgrp_id, 1)->cgroup;
> +		cgrp_id = cgroup_id(cgrp);
> +#endif
> +		data->cgroup = cgrp_id;
> +	}

Would it make more sense to refuse SAMPLE_CGROUP if !CGROUP_PERF?