On Fri, Sep 23, 2016 at 01:20:09PM -0400, Thor Lancelot Simon wrote:
> On Fri, Sep 23, 2016 at 05:15:16PM +0000, Eric Haszlakiewicz wrote:
> > On September 23, 2016 10:51:30 AM EDT, Warner Losh <i...@bsdimp.com> wrote:
> > >All NCQ gives you is the ability to schedule multiple requests and
> > >to get notification of their completion (perhaps out of order). There's
> > >no coherency features are all in NCQ.
> >
> > This seems like the key thing needed to avoid FUA: to implement fsync() you
> > just wait for notifications of completion to be received, and once you have
> > those for all requests pending when fsync was called, or started as part of
> > the fsync, then you're done.
>
> The other key point is that -- unless SATA NCQ is radically different from
> SCSI tagged queuing in a particularly stupid way -- the rules require all
> "simple" tags to be completed before any "ordered" tag is completed. That is,
> ordered tags are barriers against all simple tags.
If I remember properly, there's only simple tags in ATA.
--
Manuel Bouyer <bou...@antioche.eu.org>
NetBSD: 26 ans d'experience feront toujours la difference
--
