Re: PATCH [0/8] qla2xxx: Summary of changes...

[James Bottomley <James.Bottomley@SteelEye.com>]

On Tue, 2004-09-07 at 02:00, Arjan van de Ven wrote:
> I found a "funky" bug the other day with this driver; I was testing on a
> RAID device of which I won't mention the vendor, but it had the habit of
> returning QUEUE FULL when it's internal queue was full, with multiple
> luns active that could even be on a lun which had exactly zero
> outstanding IO already. The qlogic driver happily takes the number of
> outstanding commands (0) and subtracts 1 from it to guestimate the
> max... needless to say that didn't go down to well :-) Sounds like a
> bound check would make sense here...

Actually, this isn't at all unusual.  RAID devices often have a single
memory pool for all the LUN queues.  Heavy activity on a set of LUNs can
lead to no resources for a command on others.

Although we have queue full tracking, predicting the behaviour on
devices with coupled queues like this is impossible.

However, I thought the qlogic driver used the mid-layer queue full
tracking, which takes all of this into account and won't adjust the
depth below a certain number (8 I think).

James