Arbitration Fairness Control proposal

Robert Elliott relliott at hobbit.eng.hou.compaq.com
Thu Apr 1 14:14:48 PST 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* relliott at hobbit.eng.hou.compaq.com (Robert Elliott)
*
T10/99-160r0 is now on the web site.  This is on the agenda
for next week's SPI-3 meeting and (unless changed) will be on 
the May SCSI working group meeting (for the SPC-2/FCP-2 changes).


A summary follows:

We propose controlling the arbitration fairness algorithm with 
the Disconnect-Reconnect mode page (2h) by making these changes: 

* Redefine the three FA bits as a ARBITRATION FAIRNESS field, to 
be defined by the protocol standards

* In FCP-2, define the field as three bits: 
        FARd, FAWrt, FASel (same as before)

* In SPI-3, for normal arbitration, define 000b as unfair and 
    001b - 111b as fair

* In SPI-3, for quick arbitration, define the field as "drop down 
to normal arbitration every Nth time the device wins quick 
arbitration."  This will help QAS performance when non-QAS devices 
are not expected to be present.


See the document for details.  Any comments before the meeting
are welcome.

-- 
Rob Elliott      UNIX mailto:relliott at hobbit.eng.hou.compaq.com    
Houston, TX        PC mailto:Robert.Elliott at compaq.com
*
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