On Sat, 2009-08-29 at 19:03 -0400, Christoph Hellwig wrote:
>
> The commands are conceptually writes, and in the case of IDE and SCSI
> commands actually are writes. They were only reads because we thought
> that would interact better with the elevators. Now the elevators know
> about discard requests, that advantage no longer exists.
Can you drop the final sentence of that? It isn't true, and I never said
it.
s/. Now.*/, but that isn't necessary, and making them writes makes it
easier for the low-level IDE and SCSI code to cope with the fact that
the command has to be sent with a payload./
The elevators _still_ don't know about discards, and will still let
reads and writes (and discards, which are just a special case of writes)
to the same sector all cross each other on the queue unless there's some
external factor to prevent it.
--
David Woodhouse Open Source Technology Centre
[email protected] Intel Corporation
On Thu, Sep 03, 2009 at 06:52:20PM +0100, David Woodhouse wrote:
> On Sat, 2009-08-29 at 19:03 -0400, Christoph Hellwig wrote:
> >
> > The commands are conceptually writes, and in the case of IDE and SCSI
> > commands actually are writes. They were only reads because we thought
> > that would interact better with the elevators. Now the elevators know
> > about discard requests, that advantage no longer exists.
>
> Can you drop the final sentence of that? It isn't true, and I never said
> it.
No, but you wouldn't give me a changelog entry, so I had to make
something up.
> s/. Now.*/, but that isn't necessary, and making them writes makes it
> easier for the low-level IDE and SCSI code to cope with the fact that
> the command has to be sent with a payload./
Thanks.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."