RE: Avoiding deadlock in iSCSI

[Peter Johansson <PJohansson@ACM.org>]

At 08:42 AM 9/13/00, julian_satran@il.ibm.com wrote:

>Where would you suggest it should be done without violating layering 
>constraints?

Your query is a bit laconic, Julo, but to put it in the context of how to 
preserve ordering in the event of a queue full condition, I misspoke earlier.

I was under the mistaken impression that a QUEUE FULL condition resulted in 
a CHECK CONDITION and the concomitant creation of ACA.

Jim McGrath pointed out that this is not so. Of the remedies he outlined, 
of course it's possible for the initiator to refrain from issuing more than 
one ordered task at a time. This is reasonable for many environments, for 
example those in which the preponderance of tasks are unordered with the 
occasional need of an ordered task to fence some synchronization point. In 
other environments, either purely ordered or one in which a high number of 
tasks are ordered, this could be inefficient.

I like Jim's suggestion of a QACA bit because it does not lump the QUEUE 
FULL condition together with other ACA events. It wasn't clear whether Jim 
was referring to a QACA bit in a mode page or in a CDB or both.

Although this is, strictly speaking, a T10 matter, it involves interactions 
with the iSCSI protocol's capabilities and limitations and therefore would 
benefit from participation by this working group.




Regards,

Peter Johansson

Congruent Software, Inc.
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Berkeley, CA  94707

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