Mark Lord wrote:
To maximize throughput, some kind of host-queuing would be needed, or just have the driver sit in a tight loop, starting the next I/O immediately when the previous one finishes. Linux isn't that quick (yet).
I was talking on IRC with Tejun just recently. There are several controllers (and/or "situations") like this, where some amount of host queueing would permit greater throughput, even when NCQ is not supported. sata_sx4 is the most dramatic example, where host queueing could potentially increase speed by a factor of 10 or more, since it is penalized by an awful two-irq-per-command (w/ a per-host bottleneck to boot) setup. Silicon Image has a "command buffer". And overall, I designed ->qc_prep() hook separate from ->qc_issue() to enable the prepartion of multiple commands such that it only takes a simple "go" I/O to start a transaction, immediately after the previous one ends.
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