Kevin Brown wrote:
> Greg Stark wrote:
> > I think you're being misled by analyzing the write case.
> > 
> > Consider the read case. When a user process requests a block and
> > that read makes its way down to the driver level, the driver can't
> > just put it aside and wait until it's convenient. It has to go ahead
> > and issue the read right away.
> Well, strictly speaking it doesn't *have* to.  It could delay for a
> couple of milliseconds to see if other requests come in, and then
> issue the read if none do.  If there are already other requests being
> fulfilled, then it'll schedule the request in question just like the
> rest.

The idea with SCSI or any command queuing is that you don't have to wait
for another request to come in --- you can send the request as it
arrives, then if another shows up, you send that too, and the drive
optimizes the grouping at a later time, knowing what the drive is doing,
rather queueing in the kernel.

  Bruce Momjian                        |               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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