Hello Wangnan, On 10/24/2016 08:52 AM, Wang Nan wrote:
Linux 4.7 (86e7972f690c1017fd086cdfe53d8524e68c661c) introduces PERF_EVENT_IOC_PAUSE_OUTPUT feature. Document it.
Just to confirm, I presume this patch has been superseded by the one from Vince that I just applied. Cheers, Michael
Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx> Reviewed-by: Vince Weaver <vincent.weaver@xxxxxxxxx> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx> --- 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
