Hello Wang Nan, On 10/24/2016 08:52 AM, Wang Nan wrote: > Linux 4.7 (86e7972f690c1017fd086cdfe53d8524e68c661c) introduces > PERF_EVENT_IOC_PAUSE_OUTPUT feature. Document it. > > 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. Missing line breaks in the preceding line. > +In this case, the kernel will overwrite data when sample coming, unless I find that last line hard to understand. s/sample coming/a sample arrives/? > +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. That last sentence seems incomplete. I can't understand what you mean here? Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
