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Re: ata(4) and NCQ
--- On Tue, 4/19/11, Thor Lancelot Simon <tls%panix.com@localhost> wrote:
> From: Thor Lancelot Simon <tls%panix.com@localhost>
> Subject: Re: ata(4) and NCQ
> To: "Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>
> Cc: tech-kern%NetBSD.org@localhost, bouyer%NetBSD.org@localhost
> Date: Tuesday, April 19, 2011, 1:13 PM
> On Tue, Apr 19, 2011 at 07:57:56PM
> +0000, Jonathan A. Kollasch wrote:
> I believe FreeBSD ultimately ended up faking up ATA disks
> to look like
> SCSI ones, and using their existing SCSI midlayer to manage
And so, of course, does Linux.
> It would be good to avoid that. The SCSI code is
> really large.
> However, it does do what's wanted, so perhaps a careful
> examination of
> how it manages tags and openings would be a good first
> I believe the NCQ rules are much like the SCSI tag ordering
[[ discussion of scsi tags and NCQ]]
Yes, I believe they NCQ rules are deliberatly like SCSI tagged-queue rules.
> How this maps onto ATA drives and NCQ, I don't know, but
> the overall
> issues and history are worth keeping in mind.
Also that both FreeBSD and Linux took the plunge and handle ATA drives through
their SCSI mid-layer. I agree, that code is big; but maybe that alternative is
worth examiining, too.
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