Re: Compact Flash performance...

Jeff Garzik
2007-05-31T23:27:08Z

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.

Jeff