JPH0776941B2 - Data prefetch control method - Google Patents

Description

DETAILED DESCRIPTION [Overview] Regarding a data prefetch control method of prefetching data from an external storage device and storing it in a memory, the prefetch is stopped / started when the access mode is detected and the prefetch is unnecessary / necessary. In response to a read request from the access source, the read-ahead data following this read request is read from the external storage device and stored in order to improve the data reading performance and to use the memory efficiently. A cache buffer and a file pointer for storing an address for which a read request from the access source is stored, and when the read request from the access source is not stored in the cache buffer and does not exceed a predetermined number of times continuously ( Or when the read-requested address continues to the address stored in the above file pointer ) Is determined as sequential access, and prefetching is performed (or prefetching is restarted), while when the number of read requests that are not stored in the cache buffer exceeds the prescribed number of times in succession, random access is determined. Read-ahead to stop prefetching.

[Industrial application field]

The present invention relates to a data prefetch control system for prefetching data from an external storage device and storing it in a memory.
When prefetching data from a file of an external storage device and storing it in a cache buffer, it is desired to perform prefetching only when necessary (during sequential access).

[Problems to be Solved by Conventional Techniques and Inventions]

Conventionally, the determination of whether to prefetch data from a file such as a disk device and store it in the cache buffer specifies the access state (for example, sequential access or random access) at the start of use (opening) of the file. However, prefetching is performed when sequential access is specified.

However, if the access mode is not specified at the time of opening, pre-reading is unconditionally performed because the determination cannot be made, and even if the pre-reading is changed to random access in the middle and unnecessary pre-reading is continued, the pre-reading is not efficient. In addition, there is a problem that the cache buffer is used inefficiently.

An object of the present invention is to stop / start the prefetch when the access mode is detected and the prefetch is unnecessary / necessary, improve the data prefetch performance, and efficiently use the memory.

[Means for solving the problem]

 Means for solving the problems will be described with reference to FIG.

In FIG. 1, the cache buffer 1 reads the read-ahead data following the read request from the external storage device 7 and stores the read-ahead data in response to the read request from the access source.

The file pointer 4 stores the address of the read request.

[Action]

The present invention, as shown in FIG.
And a file pointer 4 are provided, and when the read request from the access source is not stored in the cache buffer 1 continuously for a predetermined number of times (or the address for which the read request is made is stored in the file pointer 4). When it is determined that the access is sequential, the prefetch is performed (or the prefetch is restarted). On the other hand, when the read request is not stored in the cache buffer 1 for a certain number of times continuously, It is determined that the access is random and the prefetch is stopped.

Therefore, it is possible to improve the data read-ahead performance and the memory usage efficiency by detecting the access form and performing the read-ahead at the time of sequential access and stopping the read-ahead at the time of random access.

〔Example〕

Next, the configuration and operation of one embodiment of the present invention will be sequentially described in detail with reference to FIGS. 1 to 3.

In FIG. 1, the memory 5 includes a CPU 6 and an external storage device 7.
It is a memory in the prefetching device located between and. In this memory 5, a cache buffer 1 for storing data prefetched from the external storage device 7, a cache buffer management unit 2 for storing information for managing the data stored in the cache buffer 1, a read request from the CPU 6 (access source) There are provided a counter 3 for counting the number of times that the generated data does not continuously exist in the cache buffer 1 and a file pointer 4 for storing a relative position (offset address) in the file for which a read request has been made.

A specific example of the configuration shown in FIG. 1 will be described with reference to FIG. Here, as the current state of the cache buffer 1, records 1 to 10 are read from the external storage device 7 and stored as shown in the figure.

: There is a read request for record 20.

: The read request of: does not exist in the cache buffer 1, so the counter 3 is set to “1” and
The record 20 requested to be read is stored in the file pointer 4.

: There is a read request for record 30.

For the read request of :, since it does not exist in the cache buffer 1, the counter 3 becomes “2”, so it is determined to be random access, the prefetch is stopped, and this re
The record 30 for which an ad request is made is stored in the file pointer 4.

: There is a read request for record 31. File pointer 4
Since the immediately preceding read request stored in the record is record “30”, the current read request is record “31”, and continuous data is read, it is determined to be sequential access, and prefetch is restarted.

As described above, when there is no data in the cache buffer 1 for a record for which a read request has been made, the random access is determined and the prefetch is stopped when the number of times exceeds a predetermined number of times (here, twice). On the other hand, when the absence of data does not exceed the predetermined number of times (here, twice) and when the read request continues to the record of the immediately preceding read request, it is determined as sequential access and prefetching / restart is performed. As a result, the data read-ahead performance can be improved.

FIG. 3 shows a flowchart for explaining the operation of the present invention.

In FIG. 3, is the initial state. For example, this is the state of the cache buffer shown in FIG.

Is a prefetch state. At first, this is regarded as a sequential access and is set in a prefetch state, and prefetched data from the external storage device 7 is stored in the cache buffer 1.

Determines whether the read-requested record is in the cache buffer 1. If yes, do. In the case of NO, since there is no read-requested data in the cache buffer 1, the counter is incremented and is performed.

Determines whether the counter is 2. In the case of YES (when the data for which the read request has been made does not exist twice in the cache buffer 1 in succession), it is determined to be random access, and the pre-reading stop state is executed. In the case of NO, it is judged as sequential access and is executed.

Determines whether the file pointer 4 is continuous from the immediately preceding read request. This determines whether or not the record for which the current read request has been issued is continuous from the record for which there was a previous read request stored in the file pointer 4. In the case of YES, it is determined to be sequential access, and the pre-reading state is set by and the pre-reading is restarted. In the case of NO, the prefetch stop state is continued with.

〔The invention's effect〕

As described above, according to the present invention, since the prefetching is performed when the access mode is detected and the sequential access is performed, and the prefetching is stopped when the random access is performed, the data prefetching performance is improved. The memory can be used efficiently.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of the present invention, FIG. 2 is an explanatory view of a concrete example of the present invention, and FIG. 3 is a flowchart for explaining the operation of the present invention. In the figure, 1 is a cache buffer, 2 is a cache buffer management unit, 3 is a counter, 4 is a file pointer, 6 is an access source CPU, and 7 is an external storage device.

Claims (1)

[Claims] 1. A data pre-reading control system for pre-reading data from an external storage device and storing it in a memory, in response to a read request from an access source, pre-read data following this read request is read from the external storage device and stored. And a file pointer (4) for storing an address for which a read request is issued from the access source, and a read request from the access source is not stored in the cache buffer (1). When the number of consecutive times does not exceed the predetermined number (or when the read request address continues to the address stored in the file pointer (4)), it is determined as sequential access and prefetching is performed (or prefetching is performed). However, the read request is not stored in the cache buffer (1). There data prefetch control method characterized by being configured to stop prefetching determines that the random access when a exceeds a predetermined number of times in succession.