[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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