Re: FUA and TCQ (was: Plan: journalling fixes for WAPBL)

[David Holland <dholland-tech%netbsd.org@localhost>]

On Fri, Sep 23, 2016 at 11:49:50AM +0200, Edgar Fu? wrote:
 > > The whole point of tagged queueing is to let you *not* set [the write 
 > > cache] bit in the mode pages and still get good performance.
 >
 > I don't get that. My understanding was that TCQ allowed the drive
 > to re-order commands within the bounds described by the tags. With
 > the write cache disabled, all write commands must hit stable
 > storage before being reported completed. So what's the point of
 > tagging with cacheing disabled?

You can have more than one in flight at a time. Typically the more you
can manage to have pending at once, the better the performance,
especially with SSDs.

-- 
David A. Holland
dholland%netbsd.org@localhost