Re: Proposal: B_ARRIER (addresses wapbl performance?)

[Thor Lancelot Simon <tls%rek.tjls.com@localhost>]

On Tue, Dec 09, 2008 at 12:56:27PM -0800, Jason Thorpe wrote:
>
> On Dec 9, 2008, at 12:23 PM, Manuel Bouyer wrote:
>
>> Sure. And you don't care much about command completion either, as
>> long as the write to disk happen in order.
>
> And the only way to ensure that is using FUA (or explicit cache  
> flushing).

But to enforce that using FUA, you have to set FUA on *every* write.

And I do not understand the "only way" in your remark above.  Under
the constraint "if WCE is set in the cache control page" I agree that
it is correct.  But as far as I can tell, if WCE is *not* set, it is
not in fact the case that using FUA is the "only way" to ensure that
writes are committed to stable storage in order -- because the tag
ordering rules require ordered tags to complete, um, well, in-order,
and if WCE is not set, commands are not supposed to complete until
the bits are on oxide.

I am sure I am misunderstanding something.  What?

Thor