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Date: Tue, 26 Jan 2016 16:25:28 +0800
From: "Wangnan (F)" <wangnan0@huawei.com>
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To: Alexei Starovoitov <ast@kernel.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>
CC: Brendan Gregg <brendan.d.gregg@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S. Miller" <davem@davemloft.net>, He Kuang <hekuang@huawei.com>,
        Jiri Olsa <jolsa@kernel.org>, 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>,
        Will Deacon <will.deacon@arm.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 50/54] perf record: Toggle overwrite ring buffer for reading
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On 2016/1/25 17:56, Wang Nan wrote:
> Reading from a overwrite ring buffer is unrelible. perf_evsel__pause()
> should be called before reading from them.
>
> Toggel overwrite_evt_paused director after receiving done or switch
> output.
>
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Signed-off-by: He Kuang <hekuang@huawei.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> ---
>   tools/perf/builtin-record.c | 77 +++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 77 insertions(+)

[SNIP]

> +static void
> +record__toggle_overwrite_evsels(struct record *rec,
> +				enum overwrite_evt_state state)
> +{

[SNIP]

> +	rec->overwrite_evt_state = state;
> +
> +	if (action == NONE)
> +		return;
> +
> +	evlist__for_each(evlist, pos) {
> +		if (!pos->overwrite)
> +			continue;
> +		perf_evsel__pause(pos, action == PAUSE);
> +	}
> +}
> +
This part is incorrect. We should pause ring buffers for each CPU
in a channel, not each evsel.

Already fixed at:

https://git.kernel.org/cgit/linux/kernel/git/pi3orama/linux.git/commit/?h=perf/overwrite&id=fe59d9c6621c60087ce7e6e269f2f15f152d6d71

Thank you.