From owner-freebsd-scsi  Fri Oct 15  0:26:50 1999
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To: parag@cgt.com (Parag Patel)
Cc: freebsd-scsi@freebsd.org
Subject: Re: Odd dmesg output or SCSI tagged-queueing problem?
References: <689.939968210@pinhead.parag.codegen.com>
From: Ville-Pertti Keinonen <will@iki.fi>
Date: 15 Oct 1999 10:26:41 +0300
In-Reply-To: parag@cgt.com's message of "15 Oct 1999 09:17:39 +0300"
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parag@cgt.com (Parag Patel) writes:

> Now I seem to remember that these IBM drives used to be displayed like
> the Quantum, that is with the string "Tagged Queueing Enabled".  I
> searched all the /var/log/messages files to see if any earlier kernel
> did display this, but nothing up to 4.0-CURRENT as of May 1999 displayed
> this string, and I've switched to running STABLE since.

There's a comment in sys/cam/cam_xpt.c about the DCAS:

        {
                /*
                 * Slow when tagged queueing is enabled.  Write performance
                 * steadily drops off with more and more concurrent
                 * transactions.  Best sequential write performance with
                 * tagged queueing turned off and write caching turned on.
                 *
                 * PR:  kern/10398
                 * Submitted by:  Hideaki Okada <hokada@@isl.melco.co.jp>
                 * Drive:  DCAS-34330 w/ "S65A" firmware.
                 *
                 * The drive with the problem had the "S65A" firmware
                 * revision, and has also been reported (by Stephen J.
                 * Roznowski <sjr@@home.net>) for a drive with the "S61A"
                 * firmware revision.
                 *
                 * Although no one has reported problems with the 2 gig
                 * version of the DCAS drive, the assumption is that it
                 * has the same problems as the 4 gig version.  Therefore
                 * this quirk entries disables tagged queueing for all
                 * DCAS drives.
                 */
                { T_DIRECT, SIP_MEDIA_FIXED, "IBM", "DCAS*", "*" },
                /*quirks*/0, /*mintags*/0, /*maxtags*/0
        },

I didn't notice this until recently, either, even though the quirk
entry has been there for a while.  I'm not quite convinced that tagged
queueing really hurts, but haven't bothered to do any testing.  The
DCAS isn't *that* fast, in any case (but other than in terms of
performance, it seems very good).


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