--- On Tue, 4/19/11, Thor Lancelot Simon <t...@panix.com> wrote:
> From: Thor Lancelot Simon <t...@panix.com> > Subject: Re: ata(4) and NCQ > To: "Jonathan A. Kollasch" <jakll...@kollasch.net> > Cc: tech-kern@NetBSD.org, bou...@netbsd.org > 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 > tags. 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 > step. > > I believe the NCQ rules are much like the SCSI tag ordering > rules: [[ 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. --Jonathan
