[3.16.y-ckt stable] Patch "perf header: Fixup reading of HEADER_NRCPUS feature" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    perf header: Fixup reading of HEADER_NRCPUS feature

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 708cd70fc7642c5ea295fe11e39b07faef30ded7 Mon Sep 17 00:00:00 2001
From: Arnaldo Carvalho de Melo <acme at redhat.com>
Date: Fri, 11 Sep 2015 12:36:12 -0300
Subject: perf header: Fixup reading of HEADER_NRCPUS feature

commit caa470475d9b59eeff093ae650800d34612c4379 upstream.

The original patch introducing this header wrote the number of CPUs available
and online in one order and then swapped those values when reading, fix it.

Before:

  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 4
  # echo 0 > /sys/devices/system/cpu/cpu2/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 3
  # echo 0 > /sys/devices/system/cpu/cpu1/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 2

After the fix, bringing back the CPUs online:

  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 2
  # nrcpus avail : 4
  # echo 1 > /sys/devices/system/cpu/cpu2/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 3
  # nrcpus avail : 4
  # echo 1 > /sys/devices/system/cpu/cpu1/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 4

Acked-by: Namhyung Kim <namhyung at kernel.org>
Cc: Adrian Hunter <adrian.hunter at intel.com>
Cc: Borislav Petkov <bp at suse.de>
Cc: David Ahern <dsahern at gmail.com>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Jiri Olsa <jolsa at kernel.org>
Cc: Kan Liang <kan.liang at intel.com>
Cc: Stephane Eranian <eranian at google.com>
Cc: Wang Nan <wangnan0 at huawei.com>
Fixes: fbe96f29ce4b ("perf tools: Make perf.data more self-descriptive (v8)")
Link: http://lkml.kernel.org/r/20150911153323.GP23511@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 tools/perf/util/header.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 893f8e2df928..96592f7bfa9f 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1715,7 +1715,7 @@ static int process_nrcpus(struct perf_file_section *section __maybe_unused,
 	if (ph->needs_swap)
 		nr = bswap_32(nr);

-	ph->env.nr_cpus_online = nr;
+	ph->env.nr_cpus_avail = nr;

 	ret = readn(fd, &nr, sizeof(nr));
 	if (ret != sizeof(nr))
@@ -1724,7 +1724,7 @@ static int process_nrcpus(struct perf_file_section *section __maybe_unused,
 	if (ph->needs_swap)
 		nr = bswap_32(nr);

-	ph->env.nr_cpus_avail = nr;
+	ph->env.nr_cpus_online = nr;
 	return 0;
 }