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
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This archive was generated by hypermail 2b29 : Thu May 15 2003 - 22:00:41 EST