linux-kernel - Re: [PATCH 16/48] perf core: Add backward attribute to perf event

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Date:	Wed, 24 Feb 2016 14:08:50 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Cody P Schafer <dev@...yps.com>,
	"David S. Miller" <davem@...emloft.net>,
	He Kuang <hekuang@...wei.com>,
	Jérémie Galarneau 
	<jeremie.galarneau@...icios.com>, Jiri Olsa <jolsa@...nel.org>,
	Kirill Smelkov <kirr@...edi.com>,
	Li Zefan <lizefan@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, pi3orama@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/48] perf core: Add backward attribute to perf event

On Mon, Feb 22, 2016 at 09:10:43AM +0000, Wang Nan wrote:

SNIP

> +	if (is_write_backward(output_event) != is_write_backward(event))
> +		goto out;
> +
> +	/*
>  	 * If both events generate aux data, they must be on the same PMU
>  	 */
>  	if (has_aux(event) && has_aux(output_event) &&
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 37c11c6..80b1fa7 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -233,6 +233,8 @@ out:
>  int perf_output_begin(struct perf_output_handle *handle,
>  		      struct perf_event *event, unsigned int size)
>  {
> +	if (unlikely(is_write_backward(event)))
> +		return __perf_output_begin(handle, event, size, true);
>  	return __perf_output_begin(handle, event, size, false);

could this be just:
	return __perf_output_begin(handle, event, size,
				   is_write_backward(event))

also not sure if it's worth to have __perf_output_begin
if the only difference to perf_output_begin is 'backward'
argument that could be figured out from the event argument
anyway

jirka