Comment # 8 on bug 1131437 from Jan Kara

OK, 4.20 results aren't stable either:

Amean      1       38.35 (   0.00%)       38.01 (   0.90%)       39.70 ( 
-3.52%)       39.47 (  -2.91%)       38.26 (   0.24%)
Amean      2       35.02 (   0.00%)       31.31 (  10.61%)       30.80 ( 
12.05%)       35.20 (  -0.50%)       34.39 (   1.81%)
Amean      4       42.70 (   0.00%)       41.81 (   2.09%)       41.64 (  
2.47%)       37.73 (  11.63%)       34.50 (  19.20%)
Stddev     1        5.17 (   0.00%)        5.29 (  -2.22%)        3.36 ( 
35.04%)        5.24 (  -1.35%)        5.19 (  -0.23%)
Stddev     2        8.41 (   0.00%)        8.55 (  -1.64%)        8.53 ( 
-1.47%)        8.31 (   1.24%)        8.71 (  -3.60%)
Stddev     4        6.49 (   0.00%)        6.54 (  -0.87%)        6.22 (  
4.14%)        7.07 (  -8.97%)        7.63 ( -17.63%)

*But* this is with SCSI_MQ driving the disk. I'll try whether the variance
won't be lower with the old block layer because upto 4.20 (including), we were
using that for SCSI devices AFAIK.