From mboxrd@z Thu Jan 1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 15565] New: SCSI Generic queueing completes commands in reverse
order
Date: Wed, 17 Mar 2010 22:33:18 GMT
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http://bugzilla.kernel.org/show_bug.cgi?id=15565
Summary: SCSI Generic queueing completes commands in reverse
order
Product: IO/Storage
Version: 2.5
Kernel Version: 2.6.18-2.6.32
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: SCSI
AssignedTo: linux-scsi@vger.kernel.org
ReportedBy: mh-linux-kernel@loup.net
Regression: No
I've noticed after queueing the first command, subsequent commands
appear to be executed and complete in reverse order. The SCSI Generic
HOWTO says "By default, read() will return the oldest completed
request that is queued up."
This could also be a performance defect if it's what's really
happening since it isn't desirable behavior if, for example, ios are
typically ordered by lba and issued one at a time by kernel to a non
queueing block device.
This reverse order behavior is trivial to reproduce; just queue 16
concurrent INQUIRY commands. The following are typical results I get
from initially queueing 16 READ_10 commands.
Completion Command # hdr.driver_duration (us)
Order
1 22 14979
2 20 14981
3 19 14982
4 17 14984
5 16 14985
6 15 14986
7 14 14988
8 12 14990
9 11 14991
10 10 14992
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