Re: [PATCH 1/2] libata: switch to using block layer tagging support

[Jeff Garzik <jeff@garzik.org>]

Mark Lord wrote:
> Gwendal Grignou wrote:
>> Jeff, you're right, I made some mistakes:
>> - Reading SiI3132 doc again, it only supports 32 command per port, so
>> the tags must be share among all the drives behind the same port.
>> But other chipset does support up to 128 commands per port.
>> - Jens' patch is working when all disks support NCQ. Only when we have
>> a mix of drives with or without NCQ we have a problem.
> ..
> 
> Along those lines, the newer Marvell chipsets support up to 128 commands
> per host port.
> 
> I seem to recall that the Pacific Digital Qstor chip
> can manage an insane number of commands -- something like
> 32 per device per PM port [eg. (15 * 32) in total per host port].
> 
> Seems to be a widespread kind of thing for non-legacy chipsets.
> Someday we really ought to beef up libata to allow host-chipset queuing
> of non-NCQ commands, too.

SAS+SATA chips do not necessarily have per-port limits at all, even.

The limit may instead be a host-wide command queue size limit, rather 
than a per-port limit.

	Jeff