zfs-patches/0012-Zpool-iostat-remove-latency-queue-scaling.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Gregor Kopka <mailfrom-github@kopka.net>
   3 Date: Wed, 26 Sep 2018 01:29:16 +0200
   4 Subject: [PATCH] Zpool iostat: remove latency/queue scaling
   5
   6 Bandwidth and iops are average per second while *_wait are averages
   7 per request for latency or, for queue depths, an instantaneous
   8 measurement at the end of an interval (according to man zpool).
   9
  10 When calculating the first two it makes sense to do
  11 x/interval_duration (x being the increase in total bytes or number of
  12 requests over the duration of the interval, interval_duration in
  13 seconds) to 'scale' from amount/interval_duration to amount/second.
  14
  15 But applying the same math for the latter (*_wait latencies/queue) is
  16 wrong as there is no interval_duration component in the values (these
  17 are time/requests to get to average_time/request or already an
  18 absulute number).
  19
  20 This bug leads to the only correct continuous *_wait figures for both
  21 latencies and queue depths from 'zpool iostat -l/q' being with
  22 duration=1 as then the wrong math cancels itself (x/1 is a nop).
  23
  24 This removes temporal scaling from latency and queue depth figures.
  25
  26 Reviewed-by: Tony Hutter <hutter2@llnl.gov>
  27 Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
  28 Signed-off-by: Gregor Kopka <gregor@kopka.net>
  29 Closes #7945
  30 Closes #7694
  31 ---
  32  cmd/zpool/zpool_main.c | 12 ++++++------
  33  1 file changed, 6 insertions(+), 6 deletions(-)
  34
  35 diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
  36 index a4fd0321..591e2e5c 100644
  37 --- a/cmd/zpool/zpool_main.c
  38 +++ b/cmd/zpool/zpool_main.c
  39 @@ -3493,7 +3493,7 @@ single_histo_average(uint64_t *histo, unsigned int buckets)
  40
  41  static void
  42  print_iostat_queues(iostat_cbdata_t *cb, nvlist_t *oldnv,
  43 -    nvlist_t *newnv, double scale)
  44 +    nvlist_t *newnv)
  45  {
  46         int i;
  47         uint64_t val;
  48 @@ -3523,7 +3523,7 @@ print_iostat_queues(iostat_cbdata_t *cb, nvlist_t *oldnv,
  49                 format = ZFS_NICENUM_1024;
  50
  51         for (i = 0; i < ARRAY_SIZE(names); i++) {
  52 -               val = nva[i].data[0] * scale;
  53 +               val = nva[i].data[0];
  54                 print_one_stat(val, format, column_width, cb->cb_scripted);
  55         }
  56
  57 @@ -3532,7 +3532,7 @@ print_iostat_queues(iostat_cbdata_t *cb, nvlist_t *oldnv,
  58
  59  static void
  60  print_iostat_latency(iostat_cbdata_t *cb, nvlist_t *oldnv,
  61 -    nvlist_t *newnv, double scale)
  62 +    nvlist_t *newnv)
  63  {
  64         int i;
  65         uint64_t val;
  66 @@ -3562,7 +3562,7 @@ print_iostat_latency(iostat_cbdata_t *cb, nvlist_t *oldnv,
  67         /* Print our avg latencies on the line */
  68         for (i = 0; i < ARRAY_SIZE(names); i++) {
  69                 /* Compute average latency for a latency histo */
  70 -               val = single_histo_average(nva[i].data, nva[i].count) * scale;
  71 +               val = single_histo_average(nva[i].data, nva[i].count);
  72                 print_one_stat(val, format, column_width, cb->cb_scripted);
  73         }
  74         free_calc_stats(nva, ARRAY_SIZE(names));
  75 @@ -3701,9 +3701,9 @@ print_vdev_stats(zpool_handle_t *zhp, const char *name, nvlist_t *oldnv,
  76                 print_iostat_default(calcvs, cb, scale);
  77         }
  78         if (cb->cb_flags & IOS_LATENCY_M)
  79 -               print_iostat_latency(cb, oldnv, newnv, scale);
  80 +               print_iostat_latency(cb, oldnv, newnv);
  81         if (cb->cb_flags & IOS_QUEUES_M)
  82 -               print_iostat_queues(cb, oldnv, newnv, scale);
  83 +               print_iostat_queues(cb, oldnv, newnv);
  84         if (cb->cb_flags & IOS_ANYHISTO_M) {
  85                 printf("\n");
  86                 print_iostat_histos(cb, oldnv, newnv, scale, name);