Electrical computers and digital processing systems: memory – Storage accessing and control – Hierarchical memories
Reexamination Certificate
2000-10-27
2004-04-13
Bragdon, Reginald G. (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Hierarchical memories
C711S118000, C711S213000, C710S029000
Reexamination Certificate
active
06721854
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a computer device with an auxiliary storage or a control method therefor, and in particular, to a device or method to enhance the overall system performance by using a cache memory.
2. Description of the Related Art
A recent computer system includes a CPU, a system memory, and auxiliary storage (external storage) represented by an HDD (Hard Disk Drive), and each of these components has a different data rate. When considering the performance of such a computer system, it is found that the HDD and other auxiliary storage are much slower than the CPU and the system memory in terms of data rate. Since the data rate of the overall system generally depends on the slower devices, any delay in these auxiliary storage devices may cause a bottleneck in the overall system performance.
To reduce a difference in speed between these devices to increase the processing speed, a computer system typically has a cache memory provided therein. The cache memory is placed, for example, between the CPU and a main storage, and any data or instruction used by the CPU once is retained in the cache memory, which is faster than the main storage. For subsequent uses, such data or instruction is read out from the cache memory and is not placed directly into the main storage to provide faster processing.
In addition, the HDD as an auxiliary storage (external storage) has a cache memory provided therein to hold some of the data stored in its magnetic disks (media) and is configured to improve its basic performance and to minimize the number of accesses to the slower media by prestoring in the cache memory some data which is expected to be requested later. When the data to be requested is thus prestored in the cache memory, the access time for the HDD does not cause a bottleneck in the overall system performance.
To predict data to be requested later, a data read-ahead algorithm called “Look Ahead” is most commonly used. The “Look Ahead” algorithm is a technique of prereading some data subsequent to the requested data (some data at larger addresses than the requested address), that is, a technique of reading some data in the area contiguous to the requested data after the data requested by a host device has been read out from the requested area.
The “Look Ahead” algorithm can minimize overhead required for processing by always prereading subsequent data, regardless of the previous request patterns. To really improve the performance through this technique, it is ideal to analyze the pattern of requests from an application or OS thoroughly for accurate prediction of subsequent requests.
An auxiliary storage represented by an HDD traces which commands have been issued and easily predicts which data are to be access-requested next. Therefore, the HDD is configured to improve the performance by prestoring thus predicted data in its internal cache memory. However, a request issued to, for example, an HDD is not a true request from the application or OS but is actually a request pattern, modified by collecting or rearranging several access requests through a hard disk controller (HDC). Thus, the HDD cannot analyze the true request pattern and it is difficult to increase the cache hit rate for reading.
An internal controller provided within the HDD or other auxiliary storage must trace commands from the host while controlling read/write accesses to a medium, which is the original task. Therefore, a thorough analysis or parsing on the pattern of requests from the application or OS may impose too large loads on the internal controller and it is indeed difficult to carry out such a thorough analysis or parsing.
SUMMARY OF THE INVENTION
The present invention has been made to solve the technical problems as described above, and it is an object of the present invention to cause the HDD or other auxiliary storage to cooperate with the HDC or other external controller in improving the overall system performance.
It is another object of the present invention to carry out a thorough analysis or parsing through the external controller based on a true request from the application or OS and to pre issue to the auxiliary storage a “speculation” request based on a true “prediction.”
It is still another object of the present invention to provide a mechanism to cancel a request being executed or an unexecuted request to minimize a possible performance deterioration which may result from a wrong prediction.
To attain these and other objects, a controller device according to an embodiment of the present invention is provided between auxiliary storage which stores data and a host device which makes an access request for access to the auxiliary storage. The controller device, which controls the auxiliary storage, comprises access request storage means for storing past access requests made by the host device, look-ahead request output means for providing to the auxiliary storage a look-ahead request for some data which is expected to be access-requested later based on the past access requests stored by the access request storage means, and cancel signal output means for providing to the auxiliary storage a cancel signal to cancel a particular look-ahead request among the look-ahead requests provided by the look-ahead request output means.
This controller device may take the form of, for example, a hard disk controller card (HDC card) provided between a PC, or host and a hard disk drive or other auxiliary storage. As an alternative form, the PC or host itself may have the function of this controller device so that the controller device is substantially provided between the host device and the auxiliary storage. The controller device may take any form if it can be discriminated from an internal controller provided in the auxiliary storage.
It is preferable that a look-ahead request for data provided by the look-ahead request output means is a non queue request that is executed immediately or a tagged queue request that is temporarily held in the auxiliary storage in a queue, since this can allow an optimal request to be transmitted to the auxiliary storage according to a predicted command.
In particular, it is advantageous that a cancel signal provided by the cancel signal output means is a cancel signal with a tag number to be canceled with respect to the tagged queue request, since this can allow an arbitrary command being executed to be canceled in order to improve the overall system performance.
Alternatively, a cancel signal provided by the cancel signal output means may be a command to extend a “No Operation” (NOP) command for an ATA-related interface with a tag number to be cancelled as an argument.
In addition, a cancel signal provided by the cancel signal output means with respect to a command being executed may be a signal to suspend only the command being executed by using a blank bit in a device control register for the ATA-related interface to issue a soft reset.
It should be appreciated that the ATA (AT Attachment), related interface may include an associated ATAPI (ATA Packet Interface) or other extended protocol.
A disk controller according to another embodiment of the present invention is connected to a disk-shaped storage which stores data and has a cache memory. The disk controller, which controls the disk-shaped storage, comprises an access request tracer for tracing a true access request made by an application program executed by a host with respect to the disk-storage directly from the application program, a speculation request determination section for determining a speculation request to be expected later based on the true access request traced by the access request tracer, and an access request issuing section for issuing to the disk-shaped storage a speculation request determined by the speculation request determination section.
It is preferable that a “true access request” is not a request modified by collecting or rearranging several access requests, but an intact request from the application program, since this can improve the accur
Asano Hideo
Colegrove Daniel James
Kanamaru Atsushi
Kao Kelvin
Kibashi Akira
Bracewell & Patterson L.L.P.
Bragdon Reginald G.
International Business Machines - Corporation
Raissinia Abdy
Vital Pierre M.
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