linux-kernel - Re: [PATCH] perf core: Introduce new ioctl options to pause and resume ring buffer

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Date:	Mon, 18 Jan 2016 13:02:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...nel.org, linux-kernel@...r.kernel.org, pi3orama@....com,
	lizefan@...wei.com, He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf core: Introduce new ioctl options to pause and
 resume ring buffer

On Mon, Jan 18, 2016 at 11:52:01AM +0000, Wang Nan wrote:

> +#define PERF_EVENT_IOC_PAUSE_OUTPUT	_IO ('$', 9)
> +#define PERF_EVENT_IOC_RESUME_OUTPUT	_IO ('$', 10)

Would not a single IOCTL with a 'boolean' parameter make more sense?

> +++ b/kernel/events/ring_buffer.c
> @@ -125,7 +125,7 @@ int perf_output_begin(struct perf_output_handle *handle,
>  	if (unlikely(!rb))
>  		goto out;
>  
> -	if (unlikely(!rb->nr_pages))
> +	if (unlikely(rb->paused))
>  		goto out;

Should we increment rb->lost in this case?