Date: Tue, 8 Apr 2003 16:15:47 +0200 From: Alexander Leidinger <Alexander@Leidinger.net> To: Dag-Erling Smorgrav <des@ofug.org> Cc: sos@freebsd.org Subject: Re: cvs commit: src/sys/dev/ata ata-all.c ata-all.h ata-chipset.cata-dma.c ata-pci.c ata-pci.h Message-ID: <20030408161547.1963e23a.Alexander@Leidinger.net> In-Reply-To: <xzpfzot9jrw.fsf@flood.ping.uio.no> References: <20030408152227.60c38ce3.Alexander@Leidinger.net> <200304081327.h38DR9XC025406@spider.deepcore.dk> <20030408153259.2a4b03ac.Alexander@Leidinger.net> <xzpfzot9jrw.fsf@flood.ping.uio.no>
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On Tue, 08 Apr 2003 15:54:43 +0200
Dag-Erling Smorgrav <des@ofug.org> wrote:
> Alexander Leidinger <Alexander@Leidinger.net> writes:
> > Does this mean we can't use ATA-TQ in situations where we would use TQ
> > without WC on a SCSI system (read: does it affect softupdates)?
>
> Tagged queueing doesn't make sense without a write cache. Think about
> it for a minute.
It doesn't make sense without some kind of a buffer, I know. With SCSI
disks you can observe a small difference between TQ with WC enabled and
TQ with WC disabled. Based upon this I concluded, that SCSI disks seems
to have a buffer for the WC (with all it's ill side effects in the
softupdates case) and another buffer for TQ.
SCSI != ATA, but why design another WC/TQ combination, if I can borrow
it from the SCSI disks...
Feel free to correct misunderstandings on my side.
Bye,
Alexander.
--
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http://www.Leidinger.net Alexander @ Leidinger.net
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