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Date: Wed, 24 Feb 2016 14:08:50 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Adrian Hunter <adrian.hunter@intel.com>,
        Cody P Schafer <dev@codyps.com>,
        "David S. Miller" <davem@davemloft.net>, He Kuang <hekuang@huawei.com>,
        =?iso-8859-1?Q?J=E9r=E9mie?= Galarneau 
	<jeremie.galarneau@efficios.com>,
        Jiri Olsa <jolsa@kernel.org>, Kirill Smelkov <kirr@nexedi.com>,
        Li Zefan <lizefan@huawei.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, pi3orama@163.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 16/48] perf core: Add backward attribute to perf event
Message-ID: <20160224130850.GA27710@krava.redhat.com>
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 <1456132275-98875-17-git-send-email-wangnan0@huawei.com>
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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