rt-patches/0025-hwlat-detector-Update-hwlat_detector-to-add-outer-lo.patch

   1 From 3686244e5446419fc92bb4b2bc154f776f3d0acb Mon Sep 17 00:00:00 2001
   2 From: Steven Rostedt <rostedt@goodmis.org>
   3 Date: Mon, 19 Aug 2013 17:33:25 -0400
   4 Subject: [PATCH 025/366] hwlat-detector: Update hwlat_detector to add outer
   5  loop detection
   6
   7 The hwlat_detector reads two timestamps in a row, then reports any
   8 gap between those calls. The problem is, it misses everything between
   9 the second reading of the time stamp to the first reading of the time stamp
  10 in the next loop. That's were most of the time is spent, which means,
  11 chances are likely that it will miss all hardware latencies. This
  12 defeats the purpose.
  13
  14 By also testing the first time stamp from the previous loop second
  15 time stamp (the outer loop), we are more likely to find a latency.
  16
  17 Setting the threshold to 1, here's what the report now looks like:
  18
  19 1347415723.0232202770   0       2
  20 1347415725.0234202822   0       2
  21 1347415727.0236202875   0       2
  22 1347415729.0238202928   0       2
  23 1347415731.0240202980   0       2
  24 1347415734.0243203061   0       2
  25 1347415736.0245203113   0       2
  26 1347415738.0247203166   2       0
  27 1347415740.0249203219   0       3
  28 1347415742.0251203272   0       3
  29 1347415743.0252203299   0       3
  30 1347415745.0254203351   0       2
  31 1347415747.0256203404   0       2
  32 1347415749.0258203457   0       2
  33 1347415751.0260203510   0       2
  34 1347415754.0263203589   0       2
  35 1347415756.0265203642   0       2
  36 1347415758.0267203695   0       2
  37 1347415760.0269203748   0       2
  38 1347415762.0271203801   0       2
  39 1347415764.0273203853   2       0
  40
  41 There's some hardware latency that takes 2 microseconds to run.
  42
  43 Signed-off-by: Steven Rostedt <srostedt@redhat.com>
  44 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
  45 ---
  46  drivers/misc/hwlat_detector.c | 32 ++++++++++++++++++++++++++------
  47  1 file changed, 26 insertions(+), 6 deletions(-)
  48
  49 diff --git a/drivers/misc/hwlat_detector.c b/drivers/misc/hwlat_detector.c
  50 index 6864f3c..c07e859 100644
  51 --- a/drivers/misc/hwlat_detector.c
  52 +++ b/drivers/misc/hwlat_detector.c
  53 @@ -143,6 +143,7 @@ static void detector_exit(void);
  54  struct sample {
  55         u64             seqnum;         /* unique sequence */
  56         u64             duration;       /* ktime delta */
  57 +       u64             outer_duration; /* ktime delta (outer loop) */
  58         struct timespec timestamp;      /* wall time */
  59         unsigned long   lost;
  60  };
  61 @@ -219,11 +220,13 @@ static struct sample *buffer_get_sample(struct sample *sample)
  62   */
  63  static int get_sample(void *unused)
  64  {
  65 -       ktime_t start, t1, t2;
  66 +       ktime_t start, t1, t2, last_t2;
  67         s64 diff, total = 0;
  68         u64 sample = 0;
  69 +       u64 outer_sample = 0;
  70         int ret = 1;
  71
  72 +       last_t2.tv64 = 0;
  73         start = ktime_get(); /* start timestamp */
  74
  75         do {
  76 @@ -231,7 +234,22 @@ static int get_sample(void *unused)
  77                 t1 = ktime_get();       /* we'll look for a discontinuity */
  78                 t2 = ktime_get();
  79
  80 +               if (last_t2.tv64) {
  81 +                       /* Check the delta from outer loop (t2 to next t1) */
  82 +                       diff = ktime_to_us(ktime_sub(t1, last_t2));
  83 +                       /* This shouldn't happen */
  84 +                       if (diff < 0) {
  85 +                               pr_err(BANNER "time running backwards\n");
  86 +                               goto out;
  87 +                       }
  88 +                       if (diff > outer_sample)
  89 +                               outer_sample = diff;
  90 +               }
  91 +               last_t2 = t2;
  92 +
  93                 total = ktime_to_us(ktime_sub(t2, start)); /* sample width */
  94 +
  95 +               /* This checks the inner loop (t1 to t2) */
  96                 diff = ktime_to_us(ktime_sub(t2, t1));     /* current diff */
  97
  98                 /* This shouldn't happen */
  99 @@ -246,12 +264,13 @@ static int get_sample(void *unused)
 100         } while (total <= data.sample_width);
 101
 102         /* If we exceed the threshold value, we have found a hardware latency */
 103 -       if (sample > data.threshold) {
 104 +       if (sample > data.threshold || outer_sample > data.threshold) {
 105                 struct sample s;
 106
 107                 data.count++;
 108                 s.seqnum = data.count;
 109                 s.duration = sample;
 110 +               s.outer_duration = outer_sample;
 111                 s.timestamp = CURRENT_TIME;
 112                 __buffer_add_sample(&s);
 113
 114 @@ -738,10 +757,11 @@ static ssize_t debug_sample_fread(struct file *filp, char __user *ubuf,
 115                 }
 116         }
 117
 118 -       len = snprintf(buf, sizeof(buf), "%010lu.%010lu\t%llu\n",
 119 -                     sample->timestamp.tv_sec,
 120 -                     sample->timestamp.tv_nsec,
 121 -                     sample->duration);
 122 +       len = snprintf(buf, sizeof(buf), "%010lu.%010lu\t%llu\t%llu\n",
 123 +                      sample->timestamp.tv_sec,
 124 +                      sample->timestamp.tv_nsec,
 125 +                      sample->duration,
 126 +                      sample->outer_duration);
 127
 128
 129         /* handling partial reads is more trouble than it's worth */
 130 --
 131 1.9.1
 132