Browse Prior Art Database

Dual ring buffer in AT HDD

IP.com Disclosure Number: IPCOM000015811D
Original Publication Date: 2002-Apr-25
Included in the Prior Art Database: 2003-Jun-21
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Abstract

Disclosed is a method to improve data cache performance in AT HDD. 1. In current AT HDD, look ahead reading won't be stopped even if write command comes in. By this function, there is a case that buffer data will be as follows.

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Dual ring buffer in AT HDD

Disclosed is a method to improve data cache performance in AT HDD.

1.

   In current AT HDD, look ahead reading won't be stopped even if write command
comes in. By this function, there is a case that buffer data will be as follows.

                           DLPAGE
Bottom HCPAGE
Top

|=========>.............|----------------|------------|

Read (Lookahead) Write Write

Like above case , if write data is exist after look ahead read data ,
microcode cannot extend the look-ahead read.

If cache hit status of later read command is "Half Hit" then "wait till
completion of look-ahead reading and restart reading at another buffer space
(to take care not to overwrite the write cached data)" will be required.

To realize this , construction of microcode will be too complicated.
So current H/W handle Half Hit as No HIT. But in 48bit feauture set , command
length is larger than buffer size. So sequential read cannot be cache hit.

If Read ring buffer and Write ring buffer are independent , microcode doesn't have to consider about relation of write cached data and read look ahead. And also condtruction of microcode could be simple.

2.

In current AT HDD , by read befoer pending write(RBPW) function , there is a
case that buffer data will be as follows.

                           DLPAGE
Bottom HCPAGE NextPage head of write
Top

------------|=========>.............| |----------------

                     Read (Lookahead) Write cached
data

Continuation of Read look ahead improves performance of cache , so look ahead
should be continued as long as po...