Date: Tue, 29 Mar 2016 14:06:09 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: kan.liang@intel.com
Cc: ak@linux.intel.com, eranian@google.com, vincent.weaver@maine.edu,
        tglx@linutronix.de, mingo@kernel.org, acme@redhat.com,
        jolsa@redhat.com, alexander.shishkin@linux.intel.com,
        ying.huang@linux.intel.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2 1/1] perf/core: don't find side-band event from all
 pmus
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On Wed, Mar 23, 2016 at 11:24:37AM -0700, kan.liang@intel.com wrote:
> The V2 patch is mainly based on Peter's suggestion. But I didn't rename
> perf_event_aux to perf_event_sb. Because it looks there are many aux things
> in the codes, e.g. AUX area in ring buffer. I'm not sure if we need to change
> all aux to sb. We may do the rename later in separate patch.

Right.. no problem doing that in a separate patch.

> +static void perf_event_sb_mask(unsigned int sb_mask,
> +			       perf_event_aux_output_cb output,
> +			       void *data)
> +{
> +	int sb;
> +
> +	for (sb = 0; sb < sb_nr; sb++) {
> +		if (!(sb_mask & (1 << sb)))
> +			continue;
> +		perf_event_sb_iterate(sb, output, data);
> +	}
> +}

> @@ -5852,7 +5910,8 @@ static void perf_event_task(struct task_struct *task,
>  
>  	perf_event_aux(perf_event_task_output,
>  		       &task_event,
> -		       task_ctx);
> +		       task_ctx,
> +		       (1 << sb_task) | (1 << sb_mmap) | (1 << sb_comm));
>  }

So one side-effect of this change is that the above event can be
delivered 3 times if you're 'lucky'.

Acme; does userspace care?