Re: Plan: journalling fixes for WAPBL

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Sep 23, 2016 at 09:38:44AM -0400, Thor Lancelot Simon wrote:
> > But anyway, from what I remember you still need the disk cache flush
> > operation for SATA, even with NCQ. It's not equivalent to the SCSI tags.
> 
> I think that's true only if you're running with write cache enabled; but
> the difference is that most ATA disks ship with it turned on by default.

all of them have it turned on by default, and you can't permanentely
disable it (you have to turn it off after each reset)

> 
> With an aggressive implementation of tag management on the host side,
> there should be no performance benefit from unconditionally enabling
> the write cache -- all the available cache should be used to stage
> writes for pending tags.  Sometimes it works.

With ATA you have only 32 tags ...

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--