Re: 2.5.69, IDE TCQ can't be enabled

[Jeff Garzik <jgarzik@pobox.com>]

On Mon, May 12, 2003 at 11:58:10AM -0600, Mudama, Eric wrote:
> The only difference between SATA TCQ and PATA TCQ is that in PATA TCQ, the
> drive doesn't report the active tag bitmap back to the host after each
> command.  Other than that they are functionally identical to my
> understanding.  (Yes, there are options like first-party DMA, but these are
> not requirements)

That's from the "drive side."  From the OS side, the ideal
implementation isn't here yet :)

Ideally there is a DMA ring of taskfiles and scatterlists.  The OS
(producer) queues these up asynchrously, and the host+devices
(consumer) executes the taskfiles in the ring.  AHCI does this.

With PATA TCQ, we only have a single scatterlist, and are forced to
have more OS-side infrastructure for command queueing, processing, etc.

As an aside, as drives and hosts get faster, we will actually want
_fewer_ interrupts (i.e. interrupt coalescing).

All this points to making the host smarter.
The drives are already pretty damn smart ;-)

	Jeff