Date: Sun, 12 Dec 1999 20:30:02 -0800 (PST) From: "Kenneth D. Merry" <ken@kdm.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/15446: Unpredictable enabling of SCSI Tagged Queueing Message-ID: <199912130430.UAA75208@freefall.freebsd.org>
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The following reply was made to PR kern/15446; it has been noted by GNATS.
From: "Kenneth D. Merry" <ken@kdm.org>
To: klh@netcom.com
Cc: freebsd-gnats-submit@FreeBSD.ORG
Subject: Re: kern/15446: Unpredictable enabling of SCSI Tagged Queueing
Date: Sun, 12 Dec 1999 21:23:16 -0700
On Sun, Dec 12, 1999 at 06:18:55PM -0800, klh@netcom.com wrote:
>
> >Number: 15446
> >Category: kern
> >Synopsis: Unpredictable enabling of SCSI Tagged Queueing
[ ... ]
> FreeBSD <hostname> 3.1-RELEASE FreeBSD 3.1-RELEASE #<n>: <buildstring> i386
> >Description:
> Whether or not a device capable of tagged queueing is actually flagged
> as such appears to be semi-random. It can be different for two identical
> drives, and can change from one boot to the next of the same kernel.
>
> For example, on one recent boot, two identical drives give this:
> da0: 10.0MB/s transfers (10.0MHz, offset 15), Tagged Queueing Enabled
> ...
> da2: 10.0MB/s transfers (10.0MHz, offset 15)
>
> In conjunction with another problem which I am filing separately (the
> possibility that the Seagate ST32550WC is broken with respect to
> tagged queueing) this causes my system to sometimes work and sometimes
> fail depending on the level of disk activity. I did not notice this
> earlier because until recently I have not significantly stressed the
> disk I/O. Now that it's a problem I've reviewed the system logs for
> the past few months and found that sometimes tagged queueing was
> enabled and sometimes not.
>
> FWIW the version of cam_xpt.c in my source tree is 1.42. There are
> a few too many things involved in the enable/disable code for me to be
> certain what is going on or whether the flags are even being initialized
> properly.
There are several ways to enable or disable tagged queueing:
- If the DQue bit in mode page 10 is set, tagged queueing will be disabled
for the drive in question. If you want to view/edit mode page 10, see
the camcontrol(8) man page for details.
- If the drive is quirked in cam_xpt.c to have 0 tags. The only Seagate
drives quirked in cam_xpt.c are the Seagate Medalist Pro drives.
Seagate's web site says that the 32550 is a 2 gig Barracuda. I've never
seen tagged queuing problems with Barracudas.
- If tagged queueing is enabled/disabled from userland via camcontrol(8).
Since this camcontrol option appeared in FreeBSD 3.2, that isn't an
option in your situation.
My guess is that somehow the tagged queueing bit is being enabled and
disabled in the drive firmware. None of the other ways of tweaking the
tagged queueing settings would explain the behavior you're seeing.
Check the settings in mode page 10 with camcontrol and see whether the
drive says tagged queueing is enabled or disabled. If the DQue bit is set,
the drive should not be reported as a tagged queueing drive in the dmesg.
If the DQue bit is set and then cleared somehow between boots on your
system, that points fairly strongly to some sort of problem with the drive.
Ken
--
Kenneth Merry
ken@kdm.org
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