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

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Message-ID: <569DA586.6070302@huawei.com>
Date:	Tue, 19 Jan 2016 10:55:02 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 2016/1/18 20:02, Peter Zijlstra wrote:
> 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?

Good suggestion.

>> +++ 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?

Not sure about this. The ring buffer is paused deliberately, shall we 
consider the
events we miss as losted events? However I'll try it in next version.

Thank you.