[BULK] - SAS Backoff Retry Priority

Gil Romo gil.romo at qlogic.com
Mon Aug 9 09:33:27 PDT 2004


* From the T10 Reflector (t10 at t10.org), posted by:
* Gil Romo <gil.romo at qlogic.com>
*
Hello Greg,

Suppose that the expander phy transmits a lower priority request after AIP to a 
SAS phy.  A SAS phy backs off by assuming that the incoming request has higher 
priority after receiving AIP.  This is the wrong decision, in this case, 
however.

Gil

> Date: Thu, 05 Aug 2004 21:15:33 -0600
> From: Greg Tabor <greg at vitesse.com>
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> Subject: Re: [BULK] - SAS Backoff Retry Priority
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> Gil,
> 
> Is your concern that the Retry Priority Status rule contradicts the 
> statement in 7.12.5:
> 
> "After an expander device transmits an AIP, it shall not transmit an 
> OPEN address frame unless it has higher arbitration priority than the 
> incoming connection request."
> 
> ?
> 
> If so, here are two points to consider:
> 
> 1. In 7.12.4.1 the definition of "arbitration priority" is changed when 
> IGNORE_AWT is set.
> 
> 2. If, in your example, expander 2 phy Y transmitted an OPEN frame after 
> AIP with a lower arbwait time than the one it received crossing on the 
> same link, then the expander to the right of expander 2 would also wind 
> up backing off and retrying the OPEN it originally forwarded to exp 2.Y 
> and set IGNORE_AWT when it rearbitrates as well.  So, the decision 
> settles into a consistent state in both expanders.
> 
> Regards,
> -- 
> ////////////////////////////////////////////////////
> // Greg Tabor - Vitesse Semiconductor Corporation //
> // voice: (719) 867-4414      fax: (719) 867-6203 //
> //            email: greg at vitesse.com             //
> ////////////////////////////////////////////////////
> 
> 
> Gil Romo wrote:
> > An expander obeying backoff retry priority could violate rules stated in 
> > subclause 7.12.5 "Expander rules and connection requests".
> > 
> > The attached document describes a scenario where this may occur.
> > 
> > ------------
> > Gilbert Romo
> > Circuits & Integration
> > QLogic Corporation, Aliso Viejo, California
> > Office: 949-389-6266
> > E-mail: gil.romo at qlogic.com
> 
> 

------------
Gilbert Romo
Circuits & Integration
QLogic Corporation, Aliso Viejo, California
Office: 949-389-6266
E-mail: gil.romo at qlogic.com

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