[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <alpine.DEB.2.11.1501081201020.25399@vincent-weaver-1.umelst.maine.edu>
Date: Thu, 8 Jan 2015 12:04:30 -0500 (EST)
From: Vince Weaver <vincent.weaver@...ne.edu>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
cc: xmtk.manpages@...il.com, linux-man@...r.kernel.org,
linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Paul Mackerras <paulus@...ba.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: [patch] perf_event_open.2 clarify the PERF_FLAG_FD_* flags
This change clarifies the behavior of the PERF_FLAG_FD_OUTPUT and
PERF_FLAG_FD_NO_GROUP flags to perf_event_open(), and removes
the related FIXME comments.
While writing tests to validate the behavior of these flags I
discovered that PERF_FLAG_FD_OUTPUT has been broken since the
2.6.35 kernel release.
Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>
diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 8bde791..7181c29 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -149,14 +149,17 @@ then
.BR execve (2).
.TP
.BR PERF_FLAG_FD_NO_GROUP
-.\" FIXME . The following sentence is unclear
-This flag allows creating an event as part of an event group but
-having no group leader.
-It is unclear why this is useful.
-.\" FIXME . So, why is it useful?
-.TP
-.BR PERF_FLAG_FD_OUTPUT
-This flag reroutes the output from an event to the group leader.
+This flag tells the event to ignore the
+.IR group_fd
+parameter except for the purpose of setting up output redirection
+using the
+.B PERF_FLAG_FD_OUTPUT
+flag.
+.TP
+.BR PERF_FLAG_FD_OUTPUT " (broken since Linux 2.6.35)."
+This flag re-routes the event's sampled output to instead
+be included in the mmap buffer of the event specified by
+.IR group_fd .
.TP
.BR PERF_FLAG_PID_CGROUP " (since Linux 2.6.39)."
This flag activates per-container system-wide monitoring.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists