Re: [PATCH] Asynchronous scan support for libata

[Jeff Garzik <jeff@garzik.org>]

Matthew Wilcox wrote:
> Can you tell me a bit more about these drivers?  Would it be possible to
> convert them to one host/many channels, which would give us the exclusion
> we want?


As a tangent, I would prefer a more "natural" representation than 
current, where there is a 1-1 correspondence between scsi_host and ATA 
controller instance, and a 1-1 correspondence between SCSI channels and 
ATA ports.

Alas _any_ change to the current setup requires special attention, 
because it is tied intimately into master/slave exclusion and scheduling.

I occasionally ponder what it would take to create an intelligent 
request scheduling framework that takes into account inflexible hardware 
bottlenecks like simplex (one command per controller, $n ports, $m 
devices), master/slave (one command port, $m devices), NCQ ($n commands 
per port, $m devices), port multipliers with their own bottlenecks, etc.

I see a lot of common code patterns in this area, but we are all sorta 
doing our own thing at a low level in drivers, because of subtle (and 
not-so-subtle) differences in hardware queueing support.

	Jeff, thinking out loud