Re: [PATCH v8 14/14] perf: add ITRACE_START record to indicate that tracing has started

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Nov 14, 2014 at 03:43:47PM +0200, Alexander Shishkin wrote:
> +++ b/include/uapi/linux/perf_event.h
> @@ -750,6 +750,17 @@ enum perf_event_type {
>  	 */
>  	PERF_RECORD_AUX				= 11,
>  
> +	/*
> +	 * Indicates that instruction trace has started
> +	 *
> +	 * struct {
> +	 *	struct perf_event_header	header;
> +	 *	u32				pid;
> +	 *	u32				tid;

The below function suggests we should have:

		struct sample_id		sample_id;

> +	 * };
> +	 */
> +	PERF_RECORD_ITRACE_START		= 12,
> +
>  	PERF_RECORD_MAX,			/* non-ABI */
>  };

> +static void perf_log_itrace_start(struct perf_event *event)
> +{
> +	struct perf_output_handle handle;
> +	struct perf_sample_data sample;
> +	struct perf_aux_event {
> +		struct perf_event_header        header;
> +		u32				pid;
> +		u32				tid;
> +	} rec;
> +	int ret;
> +
> +	if (event->parent)
> +		event = event->parent;
> +
> +	if (!(event->pmu->capabilities & PERF_PMU_CAP_ITRACE) ||
> +	    event->hw.itrace_started)
> +		return;
> +
> +	event->hw.itrace_started = 1;
> +
> +	rec.header.type	= PERF_RECORD_ITRACE_START;
> +	rec.header.misc	= 0;
> +	rec.header.size	= sizeof(rec);
> +	rec.pid	= perf_event_pid(event, current);
> +	rec.tid	= perf_event_tid(event, current);
> +
> +	perf_event_header__init_id(&rec.header, &sample, event);
> +	ret = perf_output_begin(&handle, event, rec.header.size);
> +
> +	if (ret)
> +		return;
> +
> +	perf_output_put(&handle, rec);
> +	perf_event__output_id_sample(event, &handle, &sample);
> +
> +	perf_output_end(&handle);
> +}