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
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