JPH045740A - Disk cache controlling system - Google Patents

Abstract

PURPOSE:To obtain maximum disk cache effect by replacing and storing write-in requested data in the same ranking position of a cache memory only when the existence of the above data in the cache memory is retrieved. CONSTITUTION:In the case of data write-in processing, even if a cache hit signal is outputted from a directory control part 14, substitution control to the most significant level of the write-in requested data in the cache memory 12 is not executed. The cache memory 12 can be efficiently used without carrying forward the data of high read-out request rate to a low order storage level, and data processing speed can be speeded up.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention provides a disk cache control method for controlling reading or writing of data in a cache memory in a write-through disk cache device. Regarding.

(Prior Art) For example, a computer equipped with a magnetic disk device as a data memory is provided with a disk cache device. This disk cache device is a device in which a cache memory composed of RAM, etc. is provided as an auxiliary storage area corresponding to each predetermined memory area of a magnetic disk device. By storing some of the data that is frequently accessed in cache memory, data access speed is increased.

Here, there are two types of disk Φ cache control methods: write-through method and write-back method. In the former write-through method, when there is a data write request from the host computer, the write requested data is stored in the cache memory. If data exists (cache reference), data is written to the cache memory and magnetic disk device, and if the requested data does not exist in the cache memory (cache miss), data is written only to the magnetic disk device. Write.

In addition, in the latter write-back method, data is written only to the cache memory for the time being regardless of the cache access or cache miss, and the cache data is copied to the magnetic disk device in later processing.

In other words, in the write-through method described above, data writing processing is always performed on the magnetic disk device, so data access is required only when reading data in the event of a cache hit compared to reading data from the magnetic disk device. In addition, with the write-back method described above, when reading data in the event of a cache hit and writing data to the cache memory, the speed is increased compared to data access with a magnetic disk device. It will be done. In this case, when reading and writing data to the cache memory, the storage order level in the cache memory of the data to be accessed is replaced with the highest level, which reduces the access frequency. High data will always be kept in the upper levels of cache memory.

Here, in the above-mentioned write-back type disk cache device, data access time can be increased in both data read and write processing, but the data written in the cache memory is not copied to the magnetic disk device. If a failure such as a power outage occurs before the data is stored, there is a good chance that the contents will be lost, so generally a write-through type disk cache device is used.

FIG. 5 shows data access processing for the cache memory of a conventional disk cache device using the write-through method. For example, when data D in the cache memory 10 is cache hit due to a data read request from the host computer, this Data D
is read out, and the cache memory 10
L RU (Least
The storage level of the data D is updated to the highest level by replacement control such as (RecentlyUsed). Further, when data A in the cache memory 10 is cache◆ hit due to a data write request, this data A is written to the magnetic disk device, and the storage level of data A in the cache memory 10 is set to the maximum level by the above replacement control. updated to a higher level. Here, due to the read request for data G, the cache
If there is a miss, data G is read from the magnetic disk device, and this data G is newly written to the highest level of cache memory 10 in accordance with the replacement control described above. In this case, cache memory 1
Data B stored at the lowest level of 0 will be ejected.

(Problem to be Solved by the Invention) However, in the conventional disk cache device using the write-through method, the data level in the cache memory 10 is updated in both the data read process and the write process when a cache hit occurs. Therefore, if the access frequency of write requests is high, only the written data will remain at the upper level in the cache memory 10, and the read data that exerts the effect of disk caching will be gradually replaced at the lower level. It will end up being put away. In other words, in a write-through type disk cache device, the effectiveness of the disk cache is demonstrated only when the cache hit data is read, so the cache hit data does not reach the highest level until the write process is performed. When replacement control is performed, frequently read data in the cache memory 10 is postponed to a lower level, reducing the effectiveness of the disk cache.

The present invention has been made in view of the above problems, and is a disk cache that makes it possible to obtain the maximum disk cache effect without controlling the replacement of cache hit data to a higher level at the time of a data write request. The purpose is to provide a control method.

[Configuration of the Invention (Means for Solving the Problem) In other words, the disk cache control method according to the present invention controls reading or writing of data in a cache memory in a write-through disk cache device. , a magnetic disk device, a cache memory provided corresponding to each predetermined memory area of the magnetic disk device, and data replacement means for replacing the storage order of a plurality of data stored in the cache memory. , cache data search means for searching whether or not the requested data exists in the cache memory at the time of a data read or write request;
The data is replaced and stored in the highest position of the memory, and at the time of the data write request, the data is stored in the same rank position of the cache memory only when the write requested data is found to exist in the cache memory by the cache data search means. and a cache data storage means for replacing and storing the data.

(Effect) In other words, cache
By performing data replacement control, data with a high read request rate is preferentially left in the cache memory, and data with low cache efficiency is preferentially ejected from the cache memory. - Improved memory usage efficiency.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a disk cache device 11 to which this disk cache control method is applied and its peripheral configuration.The disk cache device 11 includes a cache memory 12, a directory management table 13,
and the directory control unit 14, and the LRU information management table 15 and the LRU control unit 16, respectively, are connected to the path line 17.
connected via.

On the other hand, an external magnetic disk controller 18 is connected to the path line 17 of the disk cache device 11.
is connected to this magnetic disk controller 18,
A channel device 19 and a magnetic disk device 20 on the host combinator side are connected.

The directory management table 13 stores and manages tag information indicating which memory area of the magnetic disk device 20 is stored in which memory area of the cache memory 12. Based on the tag information stored in the directory management table 13, it is determined whether the data targeted for the read request or write request given to the magnetic disk controller 18 exists in the cache memory 12, and the cache hit is signal or cache miss signal as LRU (Least Recent
Used) Pressure is applied to the control unit 16. The LRU control unit 16 controls the replacement of the storage level of stored data in the cache memory 12 based on the LRU information stored in the LRU information management table 15. If the cache hit data is
The data read from the magnetic disk device 20 is written to the top level of the cache memory 12 even if the data is replaced and updated to the top level of the memory 12 and there is no cache hit. Furthermore, if there is a cache hit due to a write request from the channel device 19, the cache hit data is updated in the cache memory 12 without changing the storage level; if there is no cache hit, the cache hit data is stored in the magnetic disk device 20. Writing is performed only to

FIG. 2 is a flowchart showing data write processing in response to a magnetic disk write request from the channel device 19. First, in step S1, when a magnetic disk write request is made from the channel device 19 to the magnetic disk controller 18, In step S2, the directory system II1 unit 14 searches whether data corresponding to the write request exists in the cache memory 12, and if the write request data exists in the cache memory 12, the cache hit The cache miss signal is output to the LRU control unit 16 in step S3, and if the cache miss signal does not exist, the cache miss signal is output to the LRU control unit 16 in step S3. In this step S3, if the write request data exists in the cache memory 12 and the cache 0 hit signal is given to the LRU control unit 16, in step S4, the LRU control unit 16 writes the write request data in the cache memory 12. To write and update data hit in the cache without changing its storage level.

Then, in step S5, the magnetic disk controller 18 writes the data requested to be written from the channel device 9 to the magnetic disk device 20.

That is, even if a cache hit occurs in response to a write request from the channel device 19, this cache hit data is updated without being replaced to the highest storage level.

On the other hand, in step S3, the write request data does not exist in the cache memory 12, and the LRU control unit 1
If a cache miss signal is given to the cache memory 12, data is not written to the cache memory 12, and the process immediately proceeds to step S5, where the magnetic disk controller 18 writes the data requested to be written from the channel device 19. is written only to the magnetic disk device 20.

FIG. 3 shows the data replacement operation in the cache memory 12 of the disk cache device 11.
Here, it is assumed that the cache memory 12 handles data in blocks, and [A] to [G] indicate in which memory area of the magnetic disk device 20 the data in the corresponding block is stored. Use tag information.

For example, there is a data read request from the channel device 19 to the magnetic disk controller 18, and the tag information [D] corresponding to the read request data is stored in the cache memory 1.
2, when a cache hit signal is output from the directory control unit 14 to the LRU control unit 16, the LRU control unit 16 stores the block corresponding to the tag information [D] in the cache memory 12. Replace and update at the top level. The data stored in this cache memory block [D] is read out to the channel device 19 side through the magnetic disk controller 18.

In this case, data is read from the cache memory 12 without reading data from the magnetic disk drive 20, so the data access time can be shortened.

Next, to explain with reference to the flowchart of FIG.
There is a data write request for 8 (step S1), and tag information [A] corresponding to the write request data exists in the cache memory 12 (step S1).
2) When a cache hit signal is output from the directory control unit 14 to the LRU control unit 16 (step S3), the LRU control unit 16 replaces the storage level of the block corresponding to the tag information [A]. (Step S4). Then, the data stored in this cache memory block [A] will be written to the memory area [A] of the magnetic disk device 20 through the magnetic disk controller 18 (step 54).
).

In the case of this data writing process, the directory control unit 14
Even if a cache hit signal is applied from the cache memory 12, the write request data in the cache memory 12 is not replaced to the highest level, so data with a high read request ratio is not postponed to a lower storage level. The cache memory 12 can be used efficiently.

Furthermore, there is a data read request from the channel device 19 to the magnetic disk controller 18, and since tag information [G] corresponding to the read request data does not exist in the cache memory 12, the directory control 14
When a cache miss signal is output from 14 to the LRU control unit 16, the LRU control unit 16 transfers the block corresponding to the tag information [G] from the magnetic disk device 2o to the highest level of the cache memory 12. Write and update (staging). The data stored in this cache memory block [G] is then read and read to the channel device 19 side through the magnetic disk controller 18.

Here, the block [A] existing at the lowest level of the cache memory 12 is evicted.

In this case, the block [G] corresponding to the read request is newly written to the top level of the cache memory 12, and the remaining block [A] corresponding to the previous write request is written.
] or are evicted, the cache memory 1 can be used more effectively.
2 can be used.

FIG. 4 shows an example of an access pattern for blocks (a) and (b) in the cache memory. In the disk cache device described in the conventional example, even if accessed, the effect of the disk and cache is The block (a) that receives a high frequency of write requests that cannot be obtained will be located at the top of the cache memory, and the block (b) that receives a high rate of read requests and can benefit from disk caching will be located at a lower level. This makes them more likely to be put off and kicked out.

On the other hand, in the disk cache device described in the above embodiment, block (a), which frequently receives cache hits due to write requests, is not located at the upper level of the cache memory, so read requests are occasionally received. There is no fear that block (b) will be evicted, and even if the overall number of accesses is small, the effectiveness of the disk cache can be reliably exerted when a read request is made for block (b).

Therefore, according to the disk cache control method as described above, in the case of data write processing, for example, even if a cache hit signal is output from the directory control unit 14, the highest level of write request data in the cache memory 12 is Since we do not control the replacement of
The cache memory 12 can be used efficiently without deferring data with a high read request rate to a lower storage level, and data processing speed can be increased.

[Effects of the Invention] As described above, according to the present invention, reading or writing of data in the cache memory in a write-through type disk cache device is controlled, and the magnetic disk device and the magnetic disk device are connected to each other. A cache memory provided corresponding to each predetermined memory area, a data replacement means for replacing the storage order of a plurality of data stored in the cache memory, and a data replacement means for replacing the storage order of a plurality of data stored in the cache memory, and a data replacement means for replacing the storage order of a plurality of data stored in the cache memory, a cache data search means for searching whether or not the data exists in the cache memory; when the data read request is made, the read request data is replaced and stored in the top position of the cache memory; and when the data write request is made, the read request data is replaced and stored in the top position of the cache memory; cache data storage means for replacing and storing the write request data in the same rank position of the cache memory only when the cache data search means finds that the write request data exists in the cache memory; By performing cache data replacement control according to the frequency of data read requests, data with a high read request rate is preferentially left in the cache memory, and data with low cache efficiency is preferentially left in the cache memory. It will be ejected from memory, allowing maximum disk caching effectiveness.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a disk cache device and its peripheral configuration to which a disk cache control method according to an embodiment of the present invention is applied, and FIG. 2 is a block diagram showing the disk cache device and its peripheral configuration.
Flowchart showing data write processing based on the cache control method. FIG. 3 is a diagram showing data replacement operation in the cache memory based on the above-mentioned disk order cache control method. FIG. 4 shows block (a) and block in the cache memory. FIG. 5 is a diagram showing an example of the access pattern for (b), and FIG. 5 is a diagram showing data access processing for the cache memory of a conventional disk cache device using the write-through method. DESCRIPTION OF SYMBOLS 11... Disk cache device, 12... Cache memory, 13... Directory management table, 14... Directory control unit, 15... LRU information management table, 16... LR, U control Part, 17...
・Pass line, 18... magnetic disk controller,
19... Channel device, 20... Magnetic disk device. Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] In a disk cache control method for controlling reading or writing of data in a cache memory in a write-through type disk cache device, there is provided a magnetic disk device and a predetermined memory area of the magnetic disk device. cache memories provided in correspondence with each other; data replacement means for replacing the storage order of a plurality of data stored in the cache memories; and data replacement means for replacing the storage order of a plurality of data stored in the cache memories; a cache data search means for searching whether or not the cache data exists; when the data read request is made, the read request data is replaced and stored in the top position of the cache memory; and when the data write request is made, the write request data is stored in the cache memory; , cache data storage means for replacing and storing the cache data in the same rank position in the cache memory only when the data search means finds that the cache memory exists. control method.