lkml.org 
[lkml]   [2016]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3][manpages 1/2] perf_event_open.2: Document PERF_EVENT_IOC_PAUSE_OUTPUT
Date
Linux 4.7 (86e7972f690c1017fd086cdfe53d8524e68c661c) introduces
PERF_EVENT_IOC_PAUSE_OUTPUT feature. Document it.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Reviewed-by: Vince Weaver <vincent.weaver@maine.edu>
Cc: Michael Kerrisk <mtk.manpages@gmail.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
\
 
 \ /
  Last update: 2016-10-24 08:57    [W:0.058 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site