Shulou(Shulou.com)06/01 Report--

1. Overview of equipment assignment

Equipment dispatch refers to the equipment needed according to the user's request for equipment. The general criterion of distribution is to give full play to the effectiveness of the use of equipment, to keep the equipment busy as much as possible, and to prevent the formation of process deadlocks because of unreasonable methods of distribution. From the point of view of the characteristics of the equipment, the equipment identified by the following three methods are called unique equipment, shared equipment and virtual equipment.

1) exclusive use of equipment. It means that when requesting equipment, if the equipment is idle, it will be unique, other process requests will no longer be permitted, and other process requests will not be allowed until the equipment is released. For example, the printer, when using it to print, can only be used exclusively, otherwise the contents of different obligations can not be printed on the same sheet of paper.

2) time-sharing sharing equipment. When the equipment is used exclusively, the application rate of the equipment is very low, and when there is no request for the unique use of the equipment, it can be used through time-sharing to improve the application rate. For example, for the Istroke O operation of disk equipment, each request for each process can be stopped by time-sharing.

3) use the internal equipment by SPOOLing method. The SPOOLing technique is introduced during the piecemeal period of batch disposal operations, that is, the spooling Imax O technique. This technique is used for the operation of the equipment, which is essentially to stop batch disposal of the Imax O operation.

two。 Data construction of equipment dispatch

The secondary data structures of equipment dispatch include equipment control table (DCT), controller control table (COCT), channel control table (CHCT) and piecemeal equipment table (SDT). The functions of each data construction are as follows:

Equipment mastery Table DCT: set up a DCT for each equipment piecemeal, as shown in figure 5-9. It is used to record the characteristics of the equipment and the connection with the Imax O controller. DCT includes equipment identifier, equipment type, equipment shape, pointer to the master table COCT, and so on. Among them, the equipment shape guidance equipment is busy or leisure, the equipment queue pointer points to the waiting queue formed by the process of waiting for the use of the equipment, and the master table pointer points to the equipment controller connected with the equipment.

Figure 5-9 equipment mastery table

Master table COCT: each controller is equipped with a COCT, as shown in figure 5-10a. It reflects the application form of the equipment controller and the connection with the channel and so on.

Channel master table CHCT: each channel is equipped with a CHCT, as shown in figure 5-10b.

Piecemeal equipment table SDT: only one SDT for all bits and pieces, as shown in figure 5-10c. It records the status of all physical equipment that has been connected to bits and pieces, and each physical equipment occupies a table.

Figure 5-10 COCT, CHCT and SDT

Because in the piecemeal process, the number of processes is more than the number of capital, which will lead to competition for capital. Therefore, in order to have a set of reasonable allocation criteria, the secondary elements to consider are: the inherent attributes of Icano equipment, the algorithm of equipment allocation, the safety of equipment distribution and the independence of equipment.

3. Strategy of equipment distribution

1) equipment distribution criterion: equipment distribution shall be based on equipment characteristics, user requests and piecemeal equipment configuration. The general criterion of distribution should not only give full play to the effectiveness of the equipment, but also prevent the formation of a process deadlock, and separate the user procedures from the detailed equipment.

2) equipment dispatching methods: there are two methods of equipment dispatching: static dispatching and static dispatching.

Static dispatch is mainly used for the distribution of unique equipment, which distributes all the equipment, controllers (and channels) requested by the user's homework at one time before the user's homework begins to be performed. Once assigned, these equipment, controllers (and channels) will continue to be occupied by the assignment until the assignment is cancelled. The static dispatch method does not present a deadlock, but the effectiveness of the equipment is low. Therefore, the static dispatch method does not fit the general criterion of dispatch.

Static dispatch is stopped according to the performance requirements in the process of implementation. When the process requires equipment, it makes a plea for equipment to the bits and pieces through misappropriation of imperial edicts. According to the strategy of prior rules, the equipment required by the process is assigned, and the Ithumb O controller is released as soon as it is used up. The static dispatch method is beneficial to improve the application rate of equipment, but if the dispatch algorithm is not used properly, it can form a process deadlock.

3) equipment dispatching algorithm: the commonly used static equipment dispatching algorithms include begging for dispatch first, giving priority to those with high priority, and so on.

With regard to unique equipment, either static or static dispatch can be used, and static dispatch is often used, that is, this kind of equipment to be used for homework is assigned to it before the homework is performed. Shared equipment can be shared by multiple processes. Static dispatch method is commonly used, but only one process occupies it in each unit time of Icano transmission. Usually, the dispatch algorithm of begging for dispatch first and dispatching first for priority is usually used.

4. Safety of equipment distribution

The safety of equipment distribution means that the occurrence process deadlock should be avoided in equipment distribution.

1) safe dispatch method: every time the process withdraws the Ihammer O plea, it enters the congestion form and is not woken up until the completion of the Icano operation. In this way, once the process has acquired some kind of equipment, it can no longer beg for any capital, and does not insist on any capital when it is choked. Point I is the safety of equipment distribution; the flaw is that the CPU and Imax O equipment are serial tasks (for the unified process).

2) the method of unsafe allocation: the process continues to operate after withdrawing the Ithumb O request, and then withdraws the second and the third Ideband O request when the demand is needed. It enters the form of congestion only when the equipment requested by the process has been occupied by another process. The advantage is that a process can operate multiple devices at the same time, making the process agile; the disadvantage is that this equipment dispatch can cause deadlocks.

5. Mapping from logical equipment name to physical equipment name

In order to improve the sensitivity of equipment dispatch and the application rate of equipment, and to facilitate the completion of Istroke O redirection, equipment independence is introduced. Equipment independence refers to the use of program independence in the detailed use of physical equipment.

In order to achieve the independence of the equipment, the logical equipment name is used to implore the use of a certain type of equipment in the use program, and a logical equipment table (Logical Unit Table, LUT) is set up in bits and pieces, which is used to map the logical equipment name to the physical equipment name. The LUT table entry contains the logical equipment name, the physical equipment name and the equipment driver import address; when the process requests to dispatch equipment with the logical equipment name, it dispatches the response physical equipment piecemeal, and sets up a table entry in the LUT. In the future, when the process applies the logical equipment name to plead for the operation of ILUT, it looks for the physical equipment and drivers that respond by searching LUT.

There are two ways to set up a logical equipment table in bits and pieces:

Set only one LUT in all bits and pieces. In this way, the equipment distribution status of all processes is recorded in this table, so it is not allowed to have the opposite logical equipment name, which is mainly used in individual user bits and pieces.

Set up a LUT for each user. When a user logs in, bits and pieces set up a process for the user, as well as a LUT for it, and put the table into the PCB of the process.

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