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   1 From 3caeaa562733c4836e61086ec07666635006a787 Mon Sep 17 00:00:00 2001
   2 From: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
   3 Date: Mon, 7 Dec 2015 12:25:02 +0530
   4 Subject: perf kvm record/report: 'unprocessable sample' error while recording/reporting guest data
   5
   6 From: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
   7
   8 commit 3caeaa562733c4836e61086ec07666635006a787 upstream.
   9
  10 While recording guest samples in host using perf kvm record, it will
  11 populate unprocessable sample error, though samples will be recorded
  12 properly. While generating report using perf kvm report, no samples will
  13 be processed and same error will populate. We have seen this behaviour
  14 with upstream perf(4.4-rc3) on x86 and ppc64 hardware.
  15
  16 Reason behind this failure is, when it tries to fetch machine from
  17 rb_tree of machines, it fails. As a part of tracing a bug, we figured
  18 out that this code was incorrectly refactored in commit 54245fdc3576
  19 ("perf session: Remove wrappers to machines__find").
  20
  21 This patch will change the functionality such that if it can't fetch
  22 machine in first trial, it will create one node of machine and add that to
  23 rb_tree. So next time when it tries to fetch same machine from rb_tree,
  24 it won't fail. Actually it was the case before refactoring of code in
  25 aforementioned commit.
  26
  27 This patch is generated from acme perf/core branch.
  28
  29 Below I've mention an example that demonstrate the behaviour before and
  30 after applying patch.
  31
  32 Before applying patch:
  33 [Note: One needs to run guest before recording data in host]
  34
  35   ravi@ravi-bangoria:~$ ./perf kvm record -a
  36   Warning:
  37   5903 unprocessable samples recorded.
  38   Do you have a KVM guest running and not using 'perf kvm'?
  39   [ perf record: Captured and wrote 1.409 MB perf.data.guest (285 samples) ]
  40
  41   ravi@ravi-bangoria:~$ ./perf kvm report --stdio
  42   Warning:
  43   5903 unprocessable samples recorded.
  44   Do you have a KVM guest running and not using 'perf kvm'?
  45   # To display the perf.data header info, please use --header/--header-only options.
  46   #
  47   # Total Lost Samples: 0
  48   #
  49   # Samples: 285  of event 'cycles'
  50   # Event count (approx.): 88715406
  51   #
  52   # Overhead  Command  Shared Object  Symbol
  53   # ........  .......  .............  ......
  54   #
  55
  56   # (For a higher level overview, try: perf report --sort comm,dso)
  57   #
  58
  59 After applying patch:
  60
  61   ravi@ravi-bangoria:~$ ./perf kvm record -a
  62   [ perf record: Captured and wrote 1.188 MB perf.data.guest (17 samples) ]
  63
  64   ravi@ravi-bangoria:~$ ./perf kvm report --stdio
  65   # To display the perf.data header info, please use --header/--header-only options.
  66   #
  67   # Total Lost Samples: 0
  68   #
  69   # Samples: 17  of event 'cycles'
  70   # Event count (approx.): 700746
  71   #
  72   # Overhead  Command  Shared Object     Symbol
  73   # ........  .......  ................  ......................
  74   #
  75       34.19%  :5758    [unknown]         [g] 0xffffffff818682ab
  76       22.79%  :5758    [unknown]         [g] 0xffffffff812dc7f8
  77       22.79%  :5758    [unknown]         [g] 0xffffffff818650d0
  78       14.83%  :5758    [unknown]         [g] 0xffffffff8161a1b6
  79        2.49%  :5758    [unknown]         [g] 0xffffffff818692bf
  80        0.48%  :5758    [unknown]         [g] 0xffffffff81869253
  81        0.05%  :5758    [unknown]         [g] 0xffffffff81869250
  82
  83 Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
  84 Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
  85 Fixes: 54245fdc3576 ("perf session: Remove wrappers to machines__find")
  86 Link: http://lkml.kernel.org/r/1449471302-11283-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com
  87 Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
  88 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  89
  90 ---
  91  tools/perf/util/session.c |    2 +-
  92  1 file changed, 1 insertion(+), 1 deletion(-)
  93
  94 --- a/tools/perf/util/session.c
  95 +++ b/tools/perf/util/session.c
  96 @@ -972,7 +972,7 @@ static struct machine *machines__find_fo
  97
  98                 machine = machines__find(machines, pid);
  99                 if (!machine)
 100 -                       machine = machines__find(machines, DEFAULT_GUEST_KERNEL_ID);
 101 +                       machine = machines__findnew(machines, DEFAULT_GUEST_KERNEL_ID);
 102                 return machine;
 103         }
 104