JPH0792730B2 - Data prefetch control method - Google Patents

Description

DETAILED DESCRIPTION [Table of Contents] Outline Industrial field of application Conventional technology (Fig. 5) Problem to be solved by the invention Means for solving the problem (Fig. 1) Operation Example (Fig. 2) ~ Fig. 4) Effect of the invention [Overview] Regarding a data prefetch control method, when a read command is executed, at least a predetermined amount of data subsequent to the read data is prefetched and held, and a data buffer and a disk are provided. When a data read command is issued from the host computer, the requested data is read from the external storage device to the data buffer and transferred to the host computer, and the subsequent data is transferred to the host computer. In the data processing device having the read-ahead function for reading to the data buffer, each is designated by the host computer. A storage means for entering the minimum prefetch amount and the maximum prefetch amount is provided, and during prefetching, commands issued until the minimum prefetch amount is reached and commands that do not require access to an external storage device are executed while continuing prefetching. The instruction that needs to access the external storage device is controlled so that the prefetch is kept waiting until the minimum prefetch amount is reached.

[Industrial application field]

The present invention relates to a data read control method for reading data from an external storage device such as a magnetic disk or an optical disk, and more particularly to reading requested data from a disk to a data buffer and transferring the data to a host computer, and also reading subsequent data. The present invention relates to a data prefetch control method for reading data into the data buffer.

A computer system usually has a large-capacity external storage device, and in order to speed up the computer system, high-speed access to the external storage device is essential, and high-speed access to the external storage device is required. Has been done.

In a small-to-medium-sized computer system, when accessing an external storage device, sequential data is accessed more often than random data, and when reading sequential data, data that can be transferred at one time Due to the limited amount of, multiple instructions may have to be used in succession.

Therefore, when a data read command is issued from the host computer, the requested data is read from the disk into a data buffer composed of semiconductor memory elements and transferred to the host computer, and the subsequent data is read into the data buffer. (Prefetch), if the next command issued by the host computer is a transfer request for the data in this data buffer, the data is transferred directly from the data buffer instead of being read from the disk. A method has been proposed in which the access waiting time is apparently shortened by eliminating the rotation waiting time when reading data with a plurality of instructions (data prefetch control method).

[Conventional technology]

FIG. 5 is a diagram showing a conventional example, FIGS. 5A and 5B are diagrams showing a state of a data buffer in a conventional data prefetching method, and FIG. 5C is a diagram showing an example of a hardware configuration. In FIG. 5, reference numeral 4 is a data buffer. The data buffer 4 is connected to the magnetic disk controller 2 as in a normal computer system, and the magnetic disk controller 2 is connected to a magnetic disk 5 as an external storage device. Further, a plurality of host computers 1a and 1b are connected to the magnetic disk controller 2, and these host computers 1a and 1b are connected to the magnetic disk controller 2.
The magnetic disk 5 can be accessed via the.

In such a computer system, when a data read command is issued from the host computer 1a to the magnetic disk 5, the requested data 41 is read into the buffer 4.
After that, as shown in FIG. 5 (A), if there is no read command from the host computer 1a or another host computer 1b, the data buffer 4 becomes full until the data buffer 4 becomes full.
Data read-ahead following 41 is performed.

However, as shown in Fig. 5 (B), the requested data
If, for example, a data read command is issued from the host computer 1b during the subsequent reading of the prefetch data 42 after reading 41, the read of the prefetch data 42 is stopped and the request from the host computer 1b is immediately issued. data
Start reading 43. Thereafter, prefetching the data 44 following the data 43 until the data buffer 4 is full is the same as that shown in FIG. 5 (A).

[Problems to be Solved by the Invention]

In this way, consider the operation when a plurality of host computers 1a and 1b read sequential data when a plurality of hosts share an external storage device.

First, as the first case, a plurality of host computers
Consider the operation when 1a and 1b read sequential data.

First, the data requested by the host computer 1a is read from the magnetic disk 5 to the data buffer 4 and transferred to the host computer 1a. Next, the pre-reading of the subsequent data of the data requested by the host computer 1a is performed. At this time, when the data read command is issued from the host computer 1b, the pre-reading is stopped and the data requested by the host computer 1b is immediately issued. From the magnetic disk 5 to the data buffer 4. And the host computer 1b
When the transfer of the requested data to the host B is completed, prefetching of the subsequent data is performed. However, when the host computer 1a issues an instruction to read the subsequent data of the first read data at this time, the prefetching is performed. Control is performed to stop and immediately transfer the data requested by the host computer 1a. However, since this data is not prefetched by the required amount after the host computer 1a transfers the first requested data, the data requested for the second time must be read from the magnetic disk 5 from the beginning.

If such a situation occurs continuously, it is necessary to seek many times between the respective addresses where the data requested by the host computer 1a and the host computer 1b are written, and in order to improve the throughput of the entire system. It will be a big hindrance.

Next, as a second case, consider a case where a data read command is issued from the host computer 1a and the host computer 1b at a somewhat long interval.

For example, first, the data requested by the host computer 1a is read from the magnetic disk 5 to the data buffer 4, and then the subsequent data is preread. When the host computer 1b issues a data read command after the pre-read data is pre-read to some extent or until the data buffer 4 is full, the data requested by the host computer 1b is sent from the magnetic disk 5 to the data buffer 4 this time. Read to. Subsequently, when the subsequent data is prefetched to some extent or until the data buffer 4 becomes full, the data initially requested by the host computer 1a and the subsequent data are destroyed. Therefore, after this, the host computer
When the instruction to read the subsequent data of the first requested data is issued from 1a, the requested data cannot be immediately transferred from the data buffer 4 and must be read from the disk again.

If such a situation continues, it becomes necessary to seek many times between the addresses of the data requested by the host computer 1a and the host computer 1b.

As described above, in the case where a plurality of hosts share an external storage device, it is an object to efficiently perform data transfer between the host and the external storage device when a data read command is sequentially issued from the plurality of hosts. The data read-ahead mechanism described above has a problem that the effect may not be exhibited at all.

The present invention has been made in view of such points,
An object of the present invention is to provide a data read-ahead control method capable of shortening the access time to an external storage device by effectively using a data buffer even when a data read command is sequentially issued from a plurality of hosts. To do.

[Means for Solving the Problems]

FIG. 1 is a diagram for explaining the principle of the present invention. FIG. 1 (A) is a basic configuration diagram, and FIG. 1 (B) is a data buffer configuration diagram for explaining a basic operation.

In FIG. 1 (A), 1a and 1b are host computers, 2 is a magnetic disk controller, and 4 is a data buffer, which is composed of semiconductor memory elements. Reference numeral 5 is a magnetic disk as an external storage device. Reference numeral 3 denotes a pointer provided according to the present invention, which is incorporated in the magnetic disk control device 2 and stores the maximum read-ahead amount and the minimum read-ahead amount designated by each host computer.
The address of each data in the data buffer is stored.

In the data pre-reading method according to the present invention, as shown in FIG. 1 (B), when a data read command is issued from one host computer, for example, 1a, to the magnetic disk 5, it is first requested by the host computer 1a. The data is read from the magnetic disk to the data buffer 4 and transferred to the host, and the subsequent data is read from the magnetic disk (preread) and stored in the data buffer 4. Here, the amount of prefetched data is set to be within the range of the maximum and minimum data prefetch amounts designated by the host computer stored in the pointer 3 for each computer. The maximum prefetch amount and the minimum prefetch amount are
It is designated in advance by a plurality of hosts.

[Action]

After the requested data is read from the host computer 1a and transferred to the host computer 1a, if the same host computer 1a or another host computer 1b issues a command, this command is a command that does not require disk access. If so, it is executed while continuing to read ahead. If the host computer 1a or 1b issues a command that requires disk access before the prefetch reaches the minimum prefetch amount, the execution of the command is delayed until the prefetch reaches the minimum prefetch amount. When the read-ahead reaches the minimum read-ahead amount and a command that requires disk access before reaching the maximum read-ahead amount is issued, the read-ahead is canceled except for a specific command, for example, a read command related to the currently read-ahead data. Then, the command is immediately executed.

Here, when a data read command is issued from another host computer 1b, the data requested by the host computer 1b is stored after the pre-read data of the host computer 1a, and then the pre-read data of the host computer 1b is stored. It

Therefore, even if an instruction to read the subsequent data of the first requested data is issued from the host computer 1a, at least the prefetched data is immediately transferred to the host computer 1a without accessing the disk. You will be able to do it.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS.

FIG. 2 is a hardware configuration diagram of an embodiment of the present invention, FIG. 3 is a diagram showing a data read state to a data buffer when the data prefetch method of the present invention is applied, and FIG. It is a flowchart for operation | movement description.

In FIG. 2, 1a and 1b are host A and host B, respectively.
And is connected to the disk 5 via the magnetic disk controller 2. The magnetic disk controller 2 has two I /
It has O control units 25 and 26, a processor 21, a ROM 22, a RAM 23, and a ring buffer control unit 24. The RAM 23 is a storage unit, and a pointer unit 23-0 and a stack unit 23-1 are prepared.

The pointer unit 23-0 stores the maximum read-ahead amount and the minimum read-ahead amount for each host designated by each host in accordance with its capability and operating state, the address on the buffer 4, and the like. At this time, the maximum read-ahead amount is specified by the ratio of the host using the data buffer, and the minimum read-ahead amount is specified by the number of blocks. In this embodiment, the minimum prefetch amount of the host A is A1, the maximum prefetch amount is A2, the minimum prefetch amount of the host B is B1, and the maximum prefetch amount is B. Further, as will be described later, the stack unit 23-1 temporarily holds an instruction that allows stacking.

Reference numeral 4 is a data buffer composed of a semiconductor memory device or the like. In this embodiment, a ring structure first in first out (FIFO) buffer is used. The buffer 4 has a capacity such that data read from and written to the magnetic disk 5 can store a plurality of blocks.

FIG. 3A is a diagram showing an example of the state of the data buffer when the data prefetching method according to the present invention is executed,
This is the case where data read commands are continuously output.

First, when a data read command is issued from the host A, the data 31 requested by the host A is read from the magnetic disk 5 to the buffer 4 and transferred to the host A. Subsequently, the data 32 following the data 31 is read from the magnetic disk 5 into the buffer 4.

When the data read command is issued from the host B after the amount of the read-ahead data 32 exceeds the minimum read-ahead amount A1 of the host A, the request data 33 from the host B is read from the magnetic disk 5 to the buffer 4, and the host B Transferred to. Subsequent to that, the subsequent data 34 of the data 33 is read.

After that, when the host A issues a read command of the data 32 following the data 31, the data 32 can be immediately read from the buffer 4.

FIG. 3B is a diagram showing another example of the state of the data buffer when the data prefetching method according to the present invention is executed.

When the data read command is issued from the host A, first, the data 35 requested by the host A is read from the magnetic disk 5 to the buffer 4 and transferred to the host A, and the subsequent data 36 is read from the magnetic disk 5 to the buffer 4. . This prefetch is the minimum prefetch data amount A1 designated by host A
If a data read command is issued from the host B before reaching 0, the command is stacked in the stack unit 23-1 and the execution of this command is waited until the prefetch data amount reaches A1. When the amount of read-ahead data reaches A1, the read-ahead ends, the stacked instruction is executed, the data 37 requested by the host B is read from the disk 5 to the buffer 4, transferred to the host B, and the subsequent data 38 Is continuously read from the disk 5 to the buffer 4.

When an instruction to read the subsequent data of the first requested data is issued from the host A during the pre-reading, the pre-reading is immediately stopped, and the data requested by the host A is transferred from the buffer 4 to the host A without accessing the disk. Transfer to. At this time, if the data requested by the host A is more than the pre-read data, only the insufficient data is read from the disk and transferred to the host A. After this,
When the host B issues an instruction to read the subsequent data of the first requested data, the prefetched data in the buffer 4 is immediately transferred to the host B in the same manner.

Further, in the above case, when the buffer is full while the data requested by the host B or the read-ahead data is being stored in the buffer, the data is continuously stored from the beginning of the buffer 4 having the ring structure and is stored first. The data already transferred to the host A is destroyed, but the read-ahead data of the host A is secured in whole or to some extent, and it is used when future reading of this data is requested.

FIG. 4 is a processing flowchart for explaining the operation of the present invention.

The details of the processing are omitted because they are the same as those described above. However, during data pre-reading, an instruction issued when the minimum pre-reading amount is not reached and that does not require access to the disk is executed while continuing pre-reading. Instructions issued up to the maximum prefetch amount that do not require access to the disk are executed while continuing prefetching.

Incidentally, in the flow, the stack-permitted instruction is an instruction that requires access to the disk, such as read or write, and other instructions, for example, an instruction that confirms whether the disk is ready, The stack will not be allowed and will be immediately executed.

〔The invention's effect〕

As described above, according to the present invention, the data buffer is effectively used by the specified maximum data read-ahead amount and minimum data read-ahead amount according to the capabilities and operating states of the hosts sharing the external storage device. Therefore, it is possible to shorten the access time to the external storage device and contribute to the improvement of the processing capacity of the entire computer system.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a hardware configuration diagram of an embodiment of the present invention, FIG. 3 is a diagram showing a data read state to a data buffer of the present invention, and FIG. 5 is a flowchart showing the processing flow of FIG. 5, and FIG. 5 is a diagram showing a conventional example. 1a, 1b ...... Host 2 ...... Magnetic disk control device 3 ...... Pointer (storage device) 4 ...... Data buffer 5 ...... Magnetic disk

Claims (1)

[Claims] 1. A data buffer (4), an external storage device (5) such as a disk, and a host computer (1). When a data read command is issued from the host computer, the requested data is externally stored. In a data processing device having a read-ahead function for reading the data from the device to the data buffer and transferring the data to the host computer, and reading the subsequent data to the data buffer, the minimum read-ahead amount and the maximum read-ahead amount designated by the host computer are respectively entered. A storage means (3) is provided, and during pre-reading, an instruction issued until reaching the minimum pre-reading amount that does not need to access the external storage device is executed while continuing pre-reading, and the external storage device needs to be accessed. Some commands have a read-ahead so that the read-ahead waits until the minimum read-ahead amount is reached. Data prefetch control method, characterized in that.