estat standard deviation looks wrong

[sebroy]

Consider the following output from the nfs script:

   microseconds                                          v3/read, cached
value range                 count ------------- Distribution -------------
[20, 30)                        7 |@
[30, 40)                       12 |@@
[40, 50)                       49 |@@@@@@@
[50, 60)                       21 |@@@
[60, 70)                       32 |@@@@@
[70, 80)                       44 |@@@@@@@
[80, 90)                       31 |@@@@@
[90, 100)                      15 |@@
[100, 200)                     60 |@@@@@@@@@
[200, 300)                      6 |@
[300, 400)                      4 |@
[400, 500)                      1 |@

   microseconds                                           v3/write, sync
value range                 count ------------- Distribution -------------
[300, 400)                    398 |@
[400, 500)                   3545 |@@@@
[500, 600)                   5085 |@@@@@@
[600, 700)                   4298 |@@@@@
[700, 800)                   3261 |@@@@
[800, 900)                   2213 |@@@
[900, 1000)                  1732 |@@
[1000, 2000)                 9806 |@@@@@@@@@@@
[2000, 3000)                 3788 |@@@@
[3000, 4000)                 1929 |@@@
[4000, 5000)                 1079 |@@
[5000, 6000)                  599 |@
[6000, 7000)                  247 |@
[7000, 8000)                  115 |@
[8000, 9000)                   65 |@
[9000, 10000)                  35 |@
[10000, 20000)                 41 |@

   microseconds                                        v3/read, uncached
value range                 count ------------- Distribution -------------
[400, 500)                      1 |@
[500, 600)                     10 |@@@@@@
[600, 700)                     33 |@@@@@@@@@@@@@@@@@@@@@
[700, 800)                     11 |@@@@@@@
[800, 900)                      2 |@
[900, 1000)                     1 |@
[1000, 2000)                    2 |@
[2000, 3000)                    1 |@
[4000, 5000)                    1 |@

                                       iops(/s)  avg latency(us)       stddev(us)  throughput(k/s)
v3/read, cached                              56               88             3229              295
v3/write, sync                             7647             1439          1726695            59783
v3/read, uncached                            12              766           244436               74


                                       iops(/s)  throughput(k/s)
total                                      7724            60073

Looking at the v3/write, sync operations, the latency standard deviation (1,726,695) is higher than the ceiling of the highest latency bucket (20,000), which is mathematically impossible.