linux-kernel - [PATCH v3][manpages 1/2] perf_event_open.2: Document PERF_EVENT_IOC_PAUSE

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Message-ID: <20161024065256.160703-2-wangnan0@huawei.com>
Date:   Mon, 24 Oct 2016 06:52:55 +0000
From:   Wang Nan <wangnan0@...wei.com>
To:     <mtk.manpages@...il.com>, <vincent.weaver@...ne.edu>
CC:     <pi3orama@....com>, <linux-kernel@...r.kernel.org>,
        <lizefan@...wei.com>, <linux-man@...r.kernel.org>,
        Wang Nan <wangnan0@...wei.com>
Subject: [PATCH v3][manpages 1/2] perf_event_open.2: Document PERF_EVENT_IOC_PAUSE_OUTPUT

Linux 4.7 (86e7972f690c1017fd086cdfe53d8524e68c661c) introduces
PERF_EVENT_IOC_PAUSE_OUTPUT feature. Document it.

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Reviewed-by: Vince Weaver <vincent.weaver@...ne.edu>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
---
 man2/perf_event_open.2 | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index fade28c..561331c 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -1687,6 +1687,15 @@ the
 .I data_tail
 value should be written by user space to reflect the last read data.
 In this case, the kernel will not overwrite unread data.
+
+When the mapping is read only (without
+.BR PROT_WRITE ),
+setting .I data_tail is not allowed.
+In this case, the kernel will overwrite data when sample coming, unless
+the ring buffer is paused by a
+.BR PERF_EVENT_IOC_PAUSE_OUTPUT
+.BR ioctl (2)
+system call before reading.
 .TP
 .IR data_offset " (since Linux 4.1)"
 .\" commit e8c6deac69629c0cb97c3d3272f8631ef17f8f0f
@@ -2865,6 +2874,21 @@ The argument is a BPF program file descriptor that was created by
 a previous
 .BR bpf (2)
 system call.
+.TP
+.BR PERF_EVENT_IOC_PAUSE_OUTPUT " (since Linux 4.7)"
+.\" commit 86e7972f690c1017fd086cdfe53d8524e68c661c
+This allows pausing and resuming the event's ring-buffer. A
+paused ring-buffer does not prevent generation of samples, but simply
+discards the samples. The discarded samples are considered lost,
+causing
+.BR PERF_RECORD_LOST
+to be generated when possible.
+
+The argument is an integer. A nonzero value pauses the ring-buffer,
+zero resumes the ring-buffer.
+
+Pausing a read only ring buffer before reading from it without having
+to worry about data being overwritten.
 .SS Using prctl(2)
 A process can enable or disable all the event groups that are
 attached to it using the
-- 
2.10.1