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Scalable Coherent Interface Ring Fairness Algorithm Enhancement

IP.com Disclosure Number: IPCOM000106430D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Burton, RW: AUTHOR [+4]

Abstract

The standard Scalable Coherent Interface (SCI) can be enhanced to improve performance and still maintain network fairness. This invention discusses how the SCI network can service both the now serving number and the now serving plus one number, rather than only serving one number at a time.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 54% of the total text.

Scalable Coherent Interface Ring Fairness Algorithm Enhancement

      The standard Scalable Coherent Interface (SCI) can be enhanced
to improve performance and still maintain network fairness.  This
invention discusses how the SCI network can service both the now
serving number and the now serving plus one number, rather than only
serving one number at a time.

Three counters are used:

1.  Now Serving Counter (Now_Serve)

2.  Now Serving Plus one Counter (N1_Serve)

3.  Next Servicing counter.  (Next_Serve)

      The basic concept is that an incoming command will start out
with a number of zero.  This indicates that it is a new command and
needs to be assigned a reservation number if it can not be
immediately serviced.  The reservation number will be assigned from
the Next_Serve counter.  If the number of the incoming command is not
zero and it matches Now_Serve and a server is free, you service that
number.  Now_Serve is assigned N1_Serve and N1_Serve is incremented.
If the number matches N1_Serve and at least two servers are free, you
service that number, leave Now_Serve alone and increment N1_Serve.
If the incoming command has a reservation number and cannot be
serviced because there are no free servers or his number does not
match, the command keeps the same number and retries later.  If the
command does not already have a number and cannot be serviced it is
assigned a reservation number from Next_Serve and Next_Serve is
incremented.

      This is t...