On Thu, 2009-12-24 at 11:12 -0800, john smith wrote:
> 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
Hi John -
FYI: there is /sys/block/*/queue/nomerges - when set to one ('echo 1
> /sys/block/<dsf>/queue/nomerges) - a lot of the merging attempts are
not performed. [Note, _some_ simple merge attempts _are_ still attempted
regardless of its setting...]
Regards,
Alan
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