Bug 839027 - fcoe: disable io merging completely
fcoe: disable io merging completely
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: kernel (Show other bugs)
Unspecified Unspecified
unspecified Severity high
: rc
: ---
Assigned To: Neil Horman
Red Hat Kernel QE team
Depends On:
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Reported: 2012-07-10 13:53 EDT by Vasu Dev
Modified: 2012-10-30 07:29 EDT (History)
2 users (show)

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Last Closed: 2012-10-30 07:29:24 EDT
Type: Bug
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Description Vasu Dev 2012-07-10 13:53:04 EDT
Upstream kernel allows disabling io merging completely thru this patch:-

488991e2 : block: Added in stricter no merge semantics for block I/O

Not just fcoe, this is required to measure true IOPS for any block device.

1. setup few luns
2. run io using fio with high qd=64 for any size.
Actual results:

fio and target both would show significant mergeing.

Expected results:
No merging required to measure true IOPS.
Comment 1 Neil Horman 2012-10-30 07:29:24 EDT
This change went into 2.6.33, and is already in the  RHEL7 kernel.  Closing

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