3) The third question is why the number of fio reported "merge"(s) is greater than the number of the "ios"?
These merges are since disk is online. not during the current fio run.
Restart the machine/disk and run fio test , then fio should report
accurate merge stats.
Thanks,
-Guru
--- On Mon, 1/4/10, Alan D. Brunelle <Alan.Brunelle@xxxxxx> wrote:
From: Alan D. Brunelle <Alan.Brunelle@xxxxxx>
Subject: Re: io scheduler merges control
To: "john smith" <whalajam@xxxxxxxxx>
Cc: fio@xxxxxxxxxxxxxxx
Date: Monday, January 4, 2010, 6:34 AM
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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