Subject: Re: wd, disk write cache, sync cache, and softdep.
To: Bill Studenmund <>
From: Eric Haszlakiewicz <>
List: tech-kern
Date: 12/17/2004 01:03:41
On Thu, Dec 16, 2004 at 04:10:39PM -0800, Bill Studenmund wrote:
> While ORDERED commands are one way to do this, the big draw back with them 
> is that they impose ordering on any other write streams. Say there are two 
> other B1 and B2, and C1, C2, and C3. We don't care if it's A1, C1, B1, C2, 
> A2, A3, B2, C3 or A1, A2, A3, B1, B2, C1, C2, C3 or C1, A1, A2, B1, B2, 
> A3, C2, C3. Or any other permutation, as long as the individual orders are 
> respected. If we use FUA-type functionality, we can have up to three 
> commands outstanding at once, and we let the disk re-order them. If we use 
> ORDERED tags, we have at most one command being processed at once.

	huh?  I'm not understanding what FUA means then.  I had assumed that
setting FUA on a write means "this write must actually be written before
this command returns".  I don't see how that enforces an ordering on A1 and
A2 if A3 has that set.