linux-kernel - [patch] perf_event_open.2: PERF_RECORD_MISC_PROC_MAP_PARSE

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Date:   Mon, 17 Oct 2016 10:50:40 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
cc:     linux-man@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kan Liang <kan.liang@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: [patch] perf_event_open.2: PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT


Linux 4.2 reserved a new bit from the misc field in the perf_event_open
mmap sample buffer:
PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT

Despite being reserved in the public include/uapi/linux/perf_event.h
header file, this bit is never set by the kernel, rather it is used
internally by the userspace "perf" utility to indicate that when
attempting to parse all of the /proc/xxx/maps files for the sample
it ended up taking too long so the scan was aborted.

Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index fa8b1bd..59ad289 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -1822,6 +1822,14 @@ See also
 .BR PERF_RECORD_MISC_EXT_RESERVED " (since Linux 2.6.35)"
 .\" commit 1676b8a077c352085d52578fb4f29350b58b6e74
 This indicates there is extended data available (currently not used).
+.TP
+.B PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT
+.\" commit 930e6fcd2bcce9bcd9d4aa7e755678d33f3fe6f4
+This bit is not set by the kernel.
+It is reserved for the userspace perf utility to indicate that
+.I /proc/xxx/maps
+parsing was taking too long and stopped and thus the mmap
+records may be truncated.
 .RE
 .TP
 .I type