IOPS-reported numbers for a test vary (more than 30% in my case) from one run to another depending on kernel io scheduler merges (reported in "Disk stats/merges=reads/writes") making it hard to measure/compare performance of block drivers, for instance.
I don't see any way to turn off kernel io scheduler merges (cfq or others)
and I'd ask if you would consider adding support for it, disabling the merges per individual device, using sys-fs maybe?
If you do, adding an option to fio for controlling the merges would be useful too,
thanks,
John
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