Subject: Re: NCR Driver Problems
To: Brad Walker <bwalker@musings.com>
From: None <Chris_G_Demetriou@NIAGARA.NECTAR.CS.CMU.EDU>
List: current-users
Date: 02/07/1996 17:13:06
> > > And the best way for this to be handled is really to have the
> > > target driver query the host bus adapter (HBA) to determine if
> > > the target supports tagged commands. If the target does then the
> > > target driver should hand off as many commands as possible to the
> > > HBA. At this point the HBA deals with transfer and resolution of
> > > the commands.
> > 
> > Of course, doing this would cause serious performance, maybe software
> > problems in the case where there are multiple active controllers on
> > the SCSI bus.
> >
> 
> No it wouldn't. All I'm saying is the target queries the HBA to
> determine if it can handle the processing of tagged msgs. It it
> can then the target driver hands a cmd to the HBA. Now, if the
> HBA queue of cmds is full. Then it doesn't accept any more. But,
> the HBA takes commands and puts it into a local queue that it
> sends commands out to the SCSI bus from.

having to retry a command because a queue is full _can_ be a
performance problem, esp. with lower-end SCSI controller chips....

This solution also has ... very odd effects, in a multi-controller
environment, and can lead to complete starvation of one controller.



chris