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Zpool iostat: remove latency/queue scaling

Bandwidth and iops are average per second while *_wait are averages
per request for latency or, for queue depths, an instantaneous
measurement at the end of an interval (according to man zpool).

When calculating the first two it makes sense to do
x/interval_duration (x being the increase in total bytes or number of
requests over the duration of the interval, interval_duration in
seconds) to 'scale' from amount/interval_duration to amount/second.

But applying the same math for the latter (*_wait latencies/queue) is
wrong as there is no interval_duration component in the values (these
are time/requests to get to average_time/request or already an
absulute number).

This bug leads to the only correct continuous *_wait figures for both
latencies and queue depths from 'zpool iostat -l/q' being with
duration=1 as then the wrong math cancels itself (x/1 is a nop).

This removes temporal scaling from latency and queue depth figures.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Gregor Kopka <gregor@kopka.net>
Closes #7945 
Closes #7694
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GregorKopka authored and tonyhutter committed Sep 25, 2018
1 parent b352f17 commit 3cf583a6360feb7b29436071d0090cd7f5f7b10f
Showing with 6 additions and 6 deletions.
  1. +6 −6 cmd/zpool/zpool_main.c
@@ -3493,7 +3493,7 @@ single_histo_average(uint64_t *histo, unsigned int buckets)
static void
print_iostat_queues(iostat_cbdata_t *cb, nvlist_t *oldnv,
nvlist_t *newnv, double scale)
nvlist_t *newnv)
{
int i;
uint64_t val;
@@ -3523,7 +3523,7 @@ print_iostat_queues(iostat_cbdata_t *cb, nvlist_t *oldnv,
format = ZFS_NICENUM_1024;
for (i = 0; i < ARRAY_SIZE(names); i++) {
val = nva[i].data[0] * scale;
val = nva[i].data[0];
print_one_stat(val, format, column_width, cb->cb_scripted);
}
@@ -3532,7 +3532,7 @@ print_iostat_queues(iostat_cbdata_t *cb, nvlist_t *oldnv,
static void
print_iostat_latency(iostat_cbdata_t *cb, nvlist_t *oldnv,
nvlist_t *newnv, double scale)
nvlist_t *newnv)
{
int i;
uint64_t val;
@@ -3562,7 +3562,7 @@ print_iostat_latency(iostat_cbdata_t *cb, nvlist_t *oldnv,
/* Print our avg latencies on the line */
for (i = 0; i < ARRAY_SIZE(names); i++) {
/* Compute average latency for a latency histo */
val = single_histo_average(nva[i].data, nva[i].count) * scale;
val = single_histo_average(nva[i].data, nva[i].count);
print_one_stat(val, format, column_width, cb->cb_scripted);
}
free_calc_stats(nva, ARRAY_SIZE(names));
@@ -3701,9 +3701,9 @@ print_vdev_stats(zpool_handle_t *zhp, const char *name, nvlist_t *oldnv,
print_iostat_default(calcvs, cb, scale);
}
if (cb->cb_flags & IOS_LATENCY_M)
print_iostat_latency(cb, oldnv, newnv, scale);
print_iostat_latency(cb, oldnv, newnv);
if (cb->cb_flags & IOS_QUEUES_M)
print_iostat_queues(cb, oldnv, newnv, scale);
print_iostat_queues(cb, oldnv, newnv);
if (cb->cb_flags & IOS_ANYHISTO_M) {
printf("\n");
print_iostat_histos(cb, oldnv, newnv, scale, name);

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