linux-kernel - Re: [PATCH] perf record: Add snapshot mode support for perf's regular events

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Date:	Wed, 2 Dec 2015 16:25:33 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Yunlong Song <yunlong.song@...wei.com>
CC:	<paulus@...ba.org>, <mingo@...hat.com>, <acme@...nel.org>,
	<linux-kernel@...r.kernel.org>, <namhyung@...nel.org>,
	<ast@...nel.org>, <masami.hiramatsu.pt@...achi.com>,
	<kan.liang@...el.com>, <adrian.hunter@...el.com>,
	<jolsa@...nel.org>, <dsahern@...il.com>, <bp@...en8.de>,
	<jean.pihet@...aro.org>, <rric@...nel.org>, <xiakaixu@...wei.com>,
	<hekuang@...wei.com>
Subject: Re: [PATCH] perf record: Add snapshot mode support for perf's regular
 events

Hi Peter,

On 2015/11/25 17:27, Peter Zijlstra wrote:
> On Tue, Nov 24, 2015 at 10:00:31PM +0800, Yunlong Song wrote:
>> In our patch, we create and maintain a user space ring buffer to store
>> perf's tracing info, instead of directly writing to perf.data file as
>> before. In snapshot mode, only a SIGUSR2 signal can trigger perf to dump
>> the tracing info currently stored in the user space ring buffer to
>> perf.data file.
> I would very much like to first fix the perf overwrite mode: see
> lkml.kernel.org/r/20151023151205.GW11639@...ns.programming.kicks-ass.net
I have an idea on this problem that, is it possible to
put the size of an event at the end of it when we working
on overwrite mode? So we can backtrack every events without
too much change to ring buffer?

Thank you.

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