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

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Date:	Tue, 24 Nov 2015 22:00:31 +0800
From:	Yunlong Song <yunlong.song@...wei.com>
To:	<a.p.zijlstra@...llo.nl>, <paulus@...ba.org>, <mingo@...hat.com>,
	<acme@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, <wangnan0@...wei.com>,
	<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: [PATCH] perf record: Add snapshot mode support for perf's regular events

This idea is issued and motivated from:
https://lwn.net/Articles/650499/

After the first RFC is sent:
http://lkml.iu.edu/hypermail/linux/kernel/1509.2/04347.html

Both David Ahern and Borislav Petkov have replied to that RFC:
http://lkml.iu.edu/hypermail/linux/kernel/1509.2/04350.html
http://lkml.iu.edu/hypermail/linux/kernel/1509.2/03914.html

Thanks to David's and Borislav's advice.

However, David's perf-based scheduling daemon just makes some count when
the signal triggers perf sched, with no sample recording and has nothing
to do with perf.data. As for Borislav's persistent events, when perf
record runs, it just makes fd to attach to the persistent event to read,
and all the persistent event's tracing info will still dump to perf.data
during perf's running.

As a result, neither David's nor Borislav's patches makes the similar
snapshot mode support as what aux trace does.

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.

Yunlong Song (1):
  perf record: Add snapshot mode support for perf's regular events

 tools/perf/builtin-record.c | 181 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 170 insertions(+), 11 deletions(-)

-- 
1.8.5.2

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