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

[Doug Ledford <dledford@redhat.com>]

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. 
         1801 Varsity Dr.
         Raleigh, NC 27606