JPH0363741A - Disk cache device - Google Patents

Abstract

PURPOSE:To effectively utilize a disk cache device by automatically adjusting the amount of a cache memory to be used as the disk cache in accordance with an access condition to a disk device. CONSTITUTION:A cache memory 3020 is provided to store the copy of data stored in a disk device 4000, and a directory 3010 is provided to identify whether the copy of the data exists in the cache memory 3020 or not. Then, an access frequency detecting means 3030 is provided to detect the number of times for an access required to the disk device 4000 per unit time, and a ratio between read/write requests. A cache memory control circuit 3070 is provided to make one part of an area on the cache memory 3020 temporarily available as one part of a main memory in an electronic computer system when the access frequency is extremely decreased or the read ratio is extremely lowered. Thus, the cache memory 3020 can be used as one part of the main memory corresponding to the access condition to the disk device 4000 and the memory resource of the disk cache device can be made effective.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a disk cache device used in a computer system, and in particular to a disk cache device that adopts a write-through (store-through) method when writing data. -Relates to cache devices.

[Prior Art] In electronic computer systems, in order to reduce processing time for disk devices, a high-speed, small-capacity cache memory is provided between the main storage device and the disk device to store frequently referenced disk data. Disk cache devices that store information in a cache memory and attempt to shorten average disk access time have been generally known.

There are two methods for writing data in a disk cache device: a write-through (store-through) method in which data is written to the cache memory and to the disk device at the same time, and a write-through (store-through) method in which data is written only to the cache memory and other There is a write bank (store-in) method in which data is written to the disk device when a block is specified and the block in the cache memory where the data has been written is replaced. In consideration of power failures, etc., a write/through type is adopted.

[Problem to be solved by the invention]

The disk cache device described above has the effect of improving data transfer performance when used by a program that has a high write ratio in disk access and has high locality of referenced disk data.

However, depending on the program that uses a certain disk area as a work area, even if a disk cache device is used, there is no locality in disk data access and the read ratio is low, so the disk cache device is not used. The effect of improving data transfer efficiency may not be achieved, and the cache memory may not be used effectively.

An object of the present invention is to provide a disk cache device that can effectively use memory resources even when executing a program with low locality of disk data access and low read rate.

[Means to solve the problem]

The disk cache device of the present invention is used in a computer system equipped with one or more disk devices.

The disk cache device according to claim fil includes: a cache memory for storing a copy of data stored in the disk device; and a cache memory for storing a copy of data stored in the disk device.
A directory for identifying whether or not it exists in memory, an access frequency detection means for detecting the number of access requests per unit time and the ratio of read/write requests to the disk device, and an access frequency detection means for detecting the number of access requests per unit time and the ratio of read/write requests If the detection results show that the frequency of access to the disk device has decreased significantly, or that the read ratio has significantly decreased in the ratio of read/write requests, at least part of the area on the cache memory and a cache memory control circuit that enables use as part of the main memory of an electronic computer system.

The disk cache device according to claim (2) includes a cache memory configured using a part of a main storage device of a computer system and for storing a copy of data stored in the disk device; A directory configured using a part of the main storage area to identify whether a copy of data stored in the disk device exists in the cache memory, and access per unit time to the disk device. The access frequency detection means detects the number of requests and the ratio of read/write requests, and the detection results of the access frequency detection means indicate whether the access frequency to the disk device has decreased significantly or the ratio of read/write requests has decreased. Cache memory that allows you to temporarily reduce the area that can be used as cache memory on the main storage device and increase the area that can be used as main memory if the read ratio is found to be extremely low. It is equipped with a control circuit.

[Effect]

According to the configuration of the present invention, the amount of cache memory of the disk cache device used as a disk cache is automatically adjusted according to the access status to the disk device, and the portion not used as a disk cache is mainly used. Since it can be used as part of storage, the memory resources of the disk cache device can be used effectively even when a program with low locality of disk data access and low read rate is executed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an electronic computer system to which the present invention is applied. FIG. 1 (in al, ioo.

is CPU, 2000 is main memory (MM), 20
10 is O3, 201 which operates on the main storage device 2000)
is a driver which is a program included in 032010.

4000 is a disk device, and 3000 is a disk control device that controls input/output of the disk device 4000.

3020 is a cache memory for temporarily storing data on the disk device 4000 as a copy;
10 is a disk device 40 in the cache memory 3020
This is a directory that stores which data on 00 is stored, and each disk controller 3000
exists above.

However, the directory 3010 and the cache memory 3020 do not necessarily have to exist on the disk controller 3000; in a computer system in which a large number of disk devices are connected, the same cache memory 3020 is required for each disk device. Since memory can be shared, a part of the main storage device 2000 can be used as a cache memory 302, as shown in FIG.
0 and directory 3010.

Next, the basic operation will be explained. CPU 10
When 00 issues a read request to the disk unit W 4000 using the driver 201), the disk control device 3000 searches the directory 3010 using the address of the read request received from the driver 201) and accesses it. The data you are trying to
Check whether it exists in memory 3020.

If it exists, read the data from it and CPU1
Transfer to 00O. If the accessed data does not exist on the cache memory 3020, the data block containing the data is read from the disk device 4000, this block is stored in an appropriate block of the cache memory 3020, and the directory 3010 is updated. At the same time, the accessed data is transferred to CP UlooO.

Conversely, when the CP [1000 issues a write request to the disk device 4000, the write data is written to the disk device 4000, and if the disk device 400
When data before the location where a 0 was written is present in cache memory 3020, that block is invalidated.

This invention deals with how to adjust the amount of the cache memory 3020 of the disk cache device that can be used as a disk cache and the amount that can be used as part of the main storage device 2000, depending on the program that uses the disk cache device. Figure 1 (a)
In the configuration of a computer system such as CP 01000.1, FIG.
Main storage device 2000. Each embodiment will be described in detail using FIG. 3, which is a relational diagram of the disk control device 3000.

In FIG. 2, 3040 is a control register that stores instruction codes for the disk device 24000 such as read/write requests, 3050 is an address register that stores the address of data specified by the read/write request to the disk device 4000, and 3030 is an access frequency detection circuit (access frequency detection means in the claims) that detects the number of access requests per unit time and read ratio for the disk device W4000;
3060 is an address decoder for accessing the cache memory 3020 as part of main memory; 307
0 is the setting of the address decoder 3060 and the directory 3 based on the information of the access frequency detection circuit 3030.
a cache memory control circuit that changes the contents of 010;
3080 is a disk cache control circuit that controls the overall operation of the disk cache device, 3090 is a comparison circuit that compares the contents of the directory 3010 and the address register 3050, and 3100 is the cache memory 30.
This is a rewrite processing circuit that performs processing such as replacing the block No. 20 with a new data block, and 31) 0 is an input/output cover sofa connected to the cache memory 3020.

The smallest storage unit of the disk device 4000 is a sector,
If a block is a group of multiple times the size, the cache memory 3020 is a memory that can be addressed in sector units, and the entire cache memory 3020 is divided into multiple blocks.
Disk data is stored in blocks and accessed in sectors.

Directory 3010 is cache memory 3020
A memory with entries corresponding to blocks in the fourth block.
As shown in the figure, each entry has a cache memory 3
The address of the data block of the disk device 4000 stored in the block corresponding to 020 is stored.

The access frequency detection circuit 3030 counts the number of times each read/write request is made to the disk device W, 4000 during a predetermined period of time, calculates the number of accesses to the disk device 4000 and the read ratio, and stores the results in the disk cache. It is sent to control circuit 3080. After a predetermined period of time has elapsed, each count value is once shifted and counting begins anew.

Next, the basic operation in FIGS. 1 and 2 will be explained. When there is a read request from the CP UlooO, the driver 201) stores the address of the data in the specified disk device 4000 in the address register 3.
050, and the instruction code of the read request is stored in the control register 3040. And comparison circuit 309
0 is the contents of directory 3010 and address register 3
050, and if they match, the data to be accessed is stored in the block of cache memory 3020 corresponding to this entry, and the data is sent to CP UlooO.

If the comparison does not match, the rewriting processing circuit 3100
As a result, an empty block is taken out from the cache memory 3020. If there is no free block, a known algorithm, for example LRU (Least Receive
ntly Used), the block that was last referenced the oldest among the blocks in use is considered to be the least frequently used block, and is selected as the replacement block.

And the directory 3010 corresponding to that block
The address of the data block being accessed is written to the entry. Next, the cache memory 3020 selected by the rewrite processing circuit 3100
The block at the address indicated in the address register 3050 is read from the disk device 4000 into the block, and
It is also sent to CP UlooO at the same time.

Following the basic operation of the disk cache device, the functions of the access frequency detection circuit 3030 and cache memory control circuit 3070, which are the features of the present invention, will be explained.

The access frequency detection circuit 3030 controls the control register 304
Depending on the instruction code in 0, a predetermined time (for example, 1 minute)
It counts the number of read/write requests made to the disk device 24000, calculates the read ratio, and sends the information to the disk cache control circuit 3080 and the cache memory control circuit 3070. Here, in a program using a disk cache device, if the number of accesses and read ratio to the disk device 4000 are below a predetermined standard, the cache memory control circuit 3070
60 and directory 301O to allocate a part of cache memory 3020 as part of main memory and make it accessible. For example, directory 301
As shown in FIG. 4, each entry of 0 has a cache valid flag indicating whether the block of the cache memory 3020 corresponding to that entry is currently being used as a disk cache or as part of main memory. If the cache memory control circuit 3070 first searches for the replacement priority indication counter in the directory 3010 and performs replacement, In order to allocate the block with the highest priority as part of main memory, disable the cache enable flag,
Activate address decoder 3060 and cache
Settings are made in order to access blocks of the memory 3020. Note that allocation of the cache memory 3020 to the main memory is done in units of blocks, and the number of blocks is determined according to information such as the read ratio calculated by the access frequency detection circuit 3030. is determined by the cache memory control circuit 3070.

Additionally, when the program that uses the disk cache device is changed, the cache memory control circuit 3070
enables the cache enable flag of the directory 301O and makes the cache memory 3020 allocated as part of the main memory usable again as a disk cache, but at this time, if part of the main memory of the cache memory 3020 If you need to save the data stored in the part that was allocated as a part, what about disk storage? As soon as you write to 1f4000, the main storage device 200
032010 performs appropriate processing such as moving it to 0.

Next, an embodiment in the configuration of a computer system such as that shown in FIG. 1 (bl) will be explained using FIG. 3. In FIG.
0. An address decoder 3060 configured by cache memory 3020 and cache memory control circuit 3070 is present on main memory 2000. In operation, the CPU 1000 registers the control register 30 each time it attempts to access disk data.
At the same time as writing the instruction code to 40, main memory 200
0, and the disk data you are trying to access is in the cache memory 30.
If the data exists, it is read from the cache memory 3020, and if it does not exist, c p uioooo reads the data from the address register 3020.
The disk control device 3000 writes the address of the disk data in 050 and accesses the disk device W 4000.

The above operations are performed using program driver 2 in 032010.
01).

Here, as in the above embodiment, the access frequency detection circuit 3
030 is an instruction code in the control register 3040 to control the disk device 4 for a predetermined period of time (for example, one minute).
Counts the number of read/write requests for 000, calculates the read ratio, and stores the information on the disk.
The data is sent to cache control circuit 3080 and cache memory control circuit 3070. In a program that uses a disk cache device, disk device 1
If the number of accesses to 4000 and the read ratio are below a predetermined standard, the cache memory control circuit 307
0 is address decoder 3060. Directory 301
0 and a portion of cache memory 3020 are allocated as part of main memory and made accessible.

By controlling as described above, the disk cache device can be used effectively even when executing a program in which there is no locality in disk data access and the read rate is low.

〔Effect of the invention〕

According to this invention, the amount of the cache memory of the disk cache device to be used as disk cache is automatically adjusted according to the access status to the disk device of a program using the disk cache device, and the amount of cache memory of the disk cache device is automatically adjusted. By allocating the portion that is not used as cache as part of main memory, the disk cache device can be used effectively even when executing programs with low disk data access locality and low read ratio. be.

[Brief explanation of drawings]

1 fa+, (bl is a block diagram showing the configuration of a computer system to which this invention is applied; FIGS. 2 and 3 are block diagrams showing the configuration of an embodiment of the disk cache device of this invention; The figure is a configuration diagram showing the format of a directory.1000...CPU, 2000...Main storage device, 2010...OS.

Claims (2)

[Claims] (1) A disk cache device used in a computer system equipped with one or more disk devices for storing data as a secondary storage device, which stores a copy of the data stored in the disk device. a cache memory for storing data; a directory for identifying whether a copy of data stored in the disk device exists in the cache memory; and a directory for requesting access per unit time to the disk device. An access frequency detection means detects the number of times the disk device has been accessed and the ratio of read/write requests, and the detection results of the access frequency detection means indicate that the frequency of accesses to the disk device has decreased extremely or that the ratio of read/write requests has decreased significantly. a cache memory control circuit that allows at least a part of the area on the cache memory to be temporarily used as part of the main memory of the computer system when an extreme drop in the read ratio is observed; A disk cache device with (2) A disk cache device used in a computer system equipped with one or more disk devices for storing data as a secondary storage device, which is part of the main storage device of the computer system. a cache memory for storing a copy of data stored in the disk device, configured using an area of the main storage device; and a cache memory configured using a part of the area of the main storage device and stored in the disk device. a directory for identifying whether a copy of data exists in the cache memory; and an access frequency detection unit for detecting the number of access requests per unit time and the ratio of read/write requests to the disk device. and if it is found from the detection result of the access frequency detection means that the frequency of access to the disk device is extremely reduced or the read ratio of read/write requests is extremely reduced, A disk cache device comprising: a cache memory control circuit that makes it possible to temporarily reduce the area on the main storage device that can be used as the cache memory to increase the area that can be used as the main memory.