Date: 15 Oct 1999 10:26:41 +0300 From: Ville-Pertti Keinonen <will@iki.fi> To: parag@cgt.com (Parag Patel) Cc: freebsd-scsi@freebsd.org Subject: Re: Odd dmesg output or SCSI tagged-queueing problem? Message-ID: <86yad5jd8u.fsf@not.demophon.com> In-Reply-To: parag@cgt.com's message of "15 Oct 1999 09:17:39 %2B0300" References: <689.939968210@pinhead.parag.codegen.com>
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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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