Re: [PATCH + RFC] Beginning of some updates to scsi mid layer

Doug Ledford
2002-06-29T10:10:08Z

On Fri, Jun 28, 2002 at 06:19:59PM -0700, Jeremy Higdon wrote:
> On Jun 28, 3:39am, Doug Ledford wrote:
> >
> > Yes, the answer to this problem involves a timer. Basically what I
> > suggest (and do in my driver) is set it so that the driver waits until
> > either A) a command is completed or B) 10ms has passed before sending the
> > command back out, whichever comes first. Since most drives have had
> > plenty of time to complete one or more commands in 10ms, we assume that
> > even if we haven't got a completion yet that the drive likely has some
> > freed up resources and so we try again.
>
>
> Do you change the queue depth that you use based on a QUEUE_FULL, then?
> If so, then I presume you have some minimum, such as two or four
> commands . . . ?

There is a minimum (I think it's 8). But, more importantly, I only adjust
the queue depth if the QUEUE_FULL messages always come at some exact
depth. If the drive returns QUEUE_FULLs at differing depths, then we
assume it's a resource shortage that causes it and that reducing the queue
depth won't necessarily help.

--
Doug Ledford <dledford@redhat.com> 919-754-3700 x44233
Red Hat, Inc.
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Raleigh, NC 27606