COMPUTER SYSTEM FOR CONTROLLING VIRTUAL MACHINES

Abstract: A computer system for controlling virtual machines (VM₁-VM m ), each given a different identification number, comprises a central processing unit (1), a channel processor (3) and one or more input/output (I/O) devices (4₁-4 n ) accommodated in the channel processor, each being given any one of the different identification numbers. Mask memories (11(1)-11(m)) and I/O interruption queues (25(1)-25(m)) are provided with the same numbers as the virtual machines, each corresponding to any one of the different identification numbers. An identification memory (12) stores the identification number of a virtual machine currently in execution. An I/O start for the I/O device by the central processing unit can be carried out, accompanying the designation of the identification number to which the I/O device in question belongs. The channel processor can set an I/O interrupt request of the I/O device into the I/O interruption queue corresponding to the identification number in question when the I/O interrupt request occurs, and the central processing unit can enable the mask memory indicated by the identification number stored in the identification memory, thereby determining whether or not the interrupt of the I/O device in question is enabled.

Description: This invention relates to a computer system for controlling multiple virtual machines and, in particular, to a system for handling an input/output (I/O) interrupt generated by an I/O device during the execution of a virtual machine. In a computer system, in order to realise the effective use of system resources, it is well known to constitute a virtual machine system comprising one or more virtual machines realised by an existing real machine constituted by hardware. In the virtual machine system, each virtual machine is controlled by a virtual machine control program (hereinafter called the "VM monitor") of the real machine system. Namely, a virtual machine to which the control right of a CPU (central processing unit) has been transferred by the VM monitor is carried out by the CPU of the real machine. In this virtual machine, the system control of the virtual machine is carried out by an operating system thereof. However, when it is considered that the result of the control thereof will affect another virtual machine, the maintainability of the entire real machine system is kept by interposition of the VM monitor, etc. For example, when an I/O start for an I/O device due to an I/O instruction of the virtual machine is caused, if an I/O operation resulting from the I/O start is completed at the I/O device, the I/O device carries out an I/O interrupt for the CPU, realised by the interposition of the VM monitor. Namely, when the I/O interrupt is generated from the I/O device during an execution of the virtual machine, if the I/O interrupt is enabled, an interrupt generating process for the real machine is carried out to transfer the control right of the CPU to the VM monitor of the real machine. The VM monitor carries out an interrupt handling routine to analyse the contents of the I/O interrupt, etc., and then, if the virtual machine which has generated the I/O instruction to cause the I/O interrupt is in an interrupt enabled stated, the VM monitor simulates the generation of the I/O interrupt for the virtual machine in question to transfer the control right of the CPU to that virtual machine, whereby an interrupt handling routine is carried out in that virtual machine. As described above, the I/O interrupt in the virtual machine system must be performed with the interposition of the VM monitor, so that a time necessary for the execution of the VM monitor is required in addition to a time necessary for processing a primary task. As a result, an overhead for control of the virtual machine is increased, which reduces the processing power of the virtual machine system. Therefore, it is an object of the present invention to provide a computer system for controlling virtual machines wherein the control overhead is reduced. EP-A-0150039 describes a method for reducing the I/O simulation overhead of a virtual machine system by avoiding simulation of interrupts executed by the virtual machine monitor control program. According to the invention as claimed, there is provided a computer system for controlling virtual machines each given a different identification number, the system comprising a central processing unit; a channel processor; and one or more input/output (I/O) devices accommodated in the channel processor, and an identification memory for storing the identification number of a virtual machine currently in execution; characterised in that mask memories are provided with the same identification numbers as the virtual machines, each corresponding to any one of the different identification numbers; in that I/O interruption queues are provided with the same identification numbers as the virtual machines, each corresponding to any one of the different identification numbers; in that an I/O start for the I/O device by the central processing unit can be carried out, accompanying the designation of the identification number to which the I/O device in question belongs; in that the channel processor can set an I/O interrupt request of the I/O device into the I/O interruption queue corresponding to the identification number in question when the I/O interrupt request occurs; and in that the central processing unit can enable the mask memory indicated by the identification number stored in the identification memory, thereby determining whether or not the interrupt of the I/O device in question is enabled. Embodiments of a computer system according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing an example of a constitution of a prior art virtual machine system; Fig. 2 is a flowchart showing an interrupt handling sequence executed in the system shown in Fig. 1; Fig. 3 is a block diagram showing an embodiment of a virtual machine system according to the present invention; and Fig. 4 is a flowchart showing an interrupt handling sequence executed in the system shown in Fig. 3 To facilitate understanding of the present invention, a virtual machine system according to the prior art, and its problems, are first described with reference to Figs. 1 and 2. Figure 1 is a view showing an example of the constitution of the prior art virtual machine system. The system comprises a central processing unit (CPU) 1; a main storage 2; a channel processor 3; and I/O devices 4₁ to 4 n . The CPU 1 comprises an instruction processing unit 10 and an I/O interrupt mask register 11, etc. The mask register 11 can set information on whether the CPU 1 should enable or disable an I/O interrupt request from an I/O interruption queue 25 (described later) set by the channel processor 3. For example, the mask register 11 comprises eight mask bits 11₀ to 11₇. Each mask bit indicates the I/O interrupt enable state when logic "1" is set. The mask bits 11₀ to 11₇ correspond to subclass numbers 0 to 7 respectively, which indicate the interrupt priority. When the control right of the CPU is given to a virtual machine, the content of the mask register 11 becomes interrupt mask information for the VM monitor and is operated generally in an all "1" state. On the other hand, each virtual machine has a virtual mask register and these registers are, as will be described later, provided, for example, in each of the virtual machine control blocks 22₁ to 22 m . The channel processor 3 constituting an I/O channel accomodates a plurality of I/O devices 4₁ to 4 n . The I/O devices 4₁ to 4 n are provided with specific subchannel numbers and subclass numbers respectively. Each subchannel number designates one of the subchannels, generally a plural number controlled by the channel processor 3. The channel processor 3 has subchannel words 24 for holding control information, for every subchannel, for example, in a hardware region 23 provided in the main storage 2. The hardware region 23 is a storage region which cannot be accessed directly by the software. Each subchannel word 24 is a control block for storing the subchannel number, subchannel class, status information, and other control information. The main storage 2 includes virtual machine regions 21₁ to 21 m wherein each program of a plurality of virtual machines VM₁ to VM m realized by the real machine is stored, and virtual machine control blocks 22₁ to 22 m wherein each control data thereof is stored. The virtual machine control blocks 22₁ to 22 m incorporate virtual I/O interrupt mask registers of the virtual machines corresponding to the I/O interrupt mask register 11 of the real machine. The main storage 2 incorporates the above-mentioned VM monitor 20. Further, the main storage 2 has a hardware region 23 wherein the subchannel words 24 and the I/O interrupt queue 25 are provided. The I/O interrupt queue 25 comprises ports 25₀ to 25₇ , each corresponding to the mask bits 11₀ to 11₇ of the mask register 11 respectively and provided for each subclass. Each of the ports 25₀ to 25₇ may have a plurality of queue elements for carrying out an I/O interrupt queuing. When a plurality of interrupts are generated in the same subclass, the interrupt generated later is placed behind the last queue element. Interrupt requests for the CPU 1 are carried out by reading out the contents of the queue elements successively for every subclass, in the order of priority, whenever the interrupt is handled. Therefore, in the same subclass, the later the interrupt, the later it is handled. Each queue element has a pointer which indicates a corresponding subchannel word. With this pointer, a subchannel word related to the I/O device which has caused the I/O device interrupt is given to the CPU 1, whereby the I/O interrupt handling can be carried out. The operation of the I/O interrupt handling carried out by the system shown in Fig. 1 will be described below with reference to Fig. 2. Figure 2 is a flowchart showing an I/O interrupt handling sequence carried out by the system shown in Fig. 1. First, an I/O start for the I/O device caused by an I/O instruction of a virtual machine will be described. The CPU 1 executes a program of the VM monitor 20 in the main storage 2 to transfer the control right of the CPU to one of the programs of the virtual machine regions 21₁ to 21 m allocated for each virtual machine, so that one virtual machine may be executed. When an I/O instruction is encountered during the execution of the virtual machine, as is well known, the CPU transfers the control right to the VM monitor 20. Then, the VM monitor 20 executes an I/O instruction of the real machine to simulate the fetched I/O instruction, so that an I/O start takes place for the channel processor 3, to start an I/O operation. As is known, the I/O start caused by the I/O instruction is carried out while designating one of the subchannels, generally a plural number, controlled by the channel processor 3, at the same time, a subclass to which the I/O device belongs is designated. The channel processor 3 stores the subclass number and necessary control information in a subchannel word 24 of the subchannel designated upon the I/O start, then starts the control of the I/O operation. When the I/O operation is completed at the I/O device, a state requiring the I/O interrupt request exists. Then, the channel processor 3 stores the given status information, etc., into the subchannel word 24 of the designated subchannel, and according to the subclass number stored in that subchannel word 24, allocates a queue element indicating the interrupt demand to a port of the I/O interruption queue 25, which corresponds to the subclass number. On the other hand, as shown in the flowchart of Fig. 2, the hardware or microprogram of the instruction processing unit 10 of the CPU 1 checks the contents of the mask bits 11₀ to 11₇ of the mask register 11 in the order of priority after every completion of a macro instruction (step S20). When the content of the mask bit indicates an interrupt enabled state, i.e., "1", a port of the I/O interruption queue 25, which corresponds to the mask bit in question, is checked (step S21), and if an interrupt request is in that port, an I/O interrupt for the real machine will be generated (step S22). On the other hand, when the mask bit of the mask register 11 assumes an interrupt disabled state, or when no interrupt request exists in the port of the queue 25 although the mask bit of the mask register 11 has assumed the interrupt enabled state, the next subclass is checked in the same way (steps S20 to S23). In this way, all the subclasses are checked, and if it is judged finally that no conditions exist to necessitate the generation of the interrupt, the next instruction will be executed. When the I/O interrupt for the real machine takes place in step S22, the control right of the CPU is transferred in an ordinary way from the execution routine of the virtual machine to the VM monitor 20 of the real machine to execute an I/O interrupt handling routine by the VM monitor 20 (step S24). By this handling routine, the interrupt information is analyzed. For example, it is determined which virtual machine has issued the I/O instruction which caused the I/O interrupt, i.e., for which virtual machine the interrupt request has been generated, or whether or not the mask bit of the virtual mask register in the virtual machine control block 22 of the virtual machine which has issued the I/O instruction is in an interrupt enabled state, etc. As a result of the analysis, when the virtual mask register in question is judged to be in an interrupt enabled state (step S25), the generation of an I/O interrupt for the virtual machine in question is simulated in the following sequence: (1) The current program status word (PSW) of virtual machine is saved in virtual machine region 21; (2) Status information is stored as interrupt information; and (3) A new PSW of the virtual machine is loaded. After that, the control right of the CPU is transferred to the virtual machine in question so as to execute the virtual machine, whereby an I/O interrupt handling routine of the virtual machine is started. On the other hand, when the mask bit of the virtual mask register is judged to be in the disabled state in step S25, the interrupt information is allocated to the I/O interrupt request queue in the virtual machine control block (step S28), whereby the interrupt is held until the mask bit assumes the enabled state, and during that period, the following instruction of the previous virtual machine is executed. Subsequently, when an instruction for changing a mask bit by the virtual machine is executed, the CPU transfers the control right of the CPU to the VM monitor 20. When the mask bit assumes the enabled state, the VM monitor 20 must take the interrupt information out of the above-mentioned queue to simulate the I/O interrupt. As described above, when an I/O interrupt handling is carried out by the system shown in Fig. 1, the VM monitor interposes at the I/O interrupt to handle the interrupt, therefore the problem arises wherein the time needed for controlling the virtual machine system may be increased. A preferred embodiment of the present invention will now be explained with reference to Figs. 3 and 4. Figure 3 is a block diagram showing a virtual machine system according to the present invention. The differences between the virtual machine system shown in Fig. 3, and that shown in Fig. 1 will be described hereunder. In Fig. 3, a central processing unit (CPU) 1 has mask registers 11(l) to 11(m), each having the same function as that of the mask register shown in Fig. 1, having numbers corresponding to the numbers of the virtual machines VM₁ to VM m . The registers 11(l) to 11(m) are allocated for the virtual machines VM₁ to VM m respectively. Further, each of the virtual machines VM₁ to VM m is given an identification number respectively, and an identification register 12 for holding the identification number of a currently executed virtual machine is provided. This identification register 12 is constituted to be able to store the identification number under the control of a VM monitor 27. A mask register corresponding to a virtual machine designated by the identification number stored in the identification register 12 is selected from the mask registers 11(l) to 11(m) to assume an operable state, while the remaining mask registers assume a standby state. A hardware region 28 in a main storage 2 is provided with a group of I/O interruption queues 25(l) to 25(m) corresponding to the mask registers 11(l) to 11(m) of the CPU 1 respectively. Each of the queues 25(l) to 25(m) has the same function as that of the queue 25 described with reference to Fig. 1. A subchannel word 26 is provided with regions for storing the identification number of a virtual machine in addition to the subchannel number, the subclass number, and the status information. The operation of the system shown in Fig. 3 will be described with reference to Fig. 4, showing an I/O interrupt handling sequence carried out by the system shown in Fig. 3. The VM monitor 27 operates in the same manner as that of the prior art system, for example, to control the virtual machines and to decide which virtual machine will receive the control right of the CPU. The VM monitor 27 assigns the identification numbers for the virtual machines VM₁ to VM m respectively, and when the control right of the CPU is given to any one of the virtual machines, loads the identification number of the virtual machine in question into the identification register 12. When an I/O start caused by an I/O instruction of the virtual machine takes place, a channel processor 3 receives a subchannel designation and a subclass designation from the CPU 1 as in the case of the prior art, and at the same time, receives the identification number stored in the identification register 12, and then stores that identification number together with the subclass number, etc., into the subchannel word 26. When an I/O operation at the I/O device is completed and a state requiring an I/O interrupt request exists, predetermined status information, etc., is stored in the subchannel word 26, then a queue corresponding to the identification number of the virtual machine stored in the subchannel word 26 is selected from the queues 25(l) to 25(m). Further, in that selected queue, one of the ports 28₀ to 28₇ provided for each subclass is selected according to the subclass number stored in the subchannel word 26 to allocate a queue element indicating the interrupt request to the selected port. Thus, the interrupt request assumes an interrupt waiting state. A hardware or a micro program of an instruction processing unit 10 of the CPU 1 selects, as shown in Fig. 4, at the time of completion of one macro instruction, one mask register designated by the control register 12 from the mask registers 11(l) to 11(m), then check the mask bits of the selected mask register to judge whether the interrupt is enabled or disabled (step S30). When the mask bit assumes the interrupt enabled state, i.e., when the mask bit is "1", a port corresponding to the mask bit in the queue is checked to judge whether or not an interrupt request exists (step S31). When the I/O interrupt request exists, a process for carrying out the interrupt directly for the currently executing virtual machine designated by the identification register 12 is carried out (step S32), and thereby an interrupt handling routine of the virtual machine is started (step S33). The interrupt generating process in the step S32 is similar to that described with reference to Fig. 2. For example, the process includes a save of the current PSW, a store of status information as interrupt information, and a loading of the new PSW, etc. When it is judged that there are no interrupt requests at step S31, as described in Fig. 2, it is judged whether or not the following subclass having a lower priority exists (step S34). When such a subclass exists, steps S30 and S31 are repeated, whereby all the subclasses of the subchannel are checked in relation to whether the interrupt is enabled or disabled and whether or not the interrupt request exists. As mentioned above, the virtual machine system shown in Fig. 3 does not require the interposition of the VM monitor to simulate an I/O interrupt when the I/O interrupt of the virtual machine is carried out, so that the overhead for controlling the virtual machine system is reduced, whereby the processing power of the virtual machine system is improved. Although a preferred embodiment has been described heretofore, various modifications and alterations are possible within the scope of the present invention as claimed.

Claims: A computer system for controlling virtual machines (VM₁-VM m ) each given a different identification number, the system comprising a central processing unit (1); a channel processor (3); and one or more input/output (I/O) devices (4₁-4 n ) accommodated in the channel processor, and an identification memory (12) for storing the identification number of a virtual machine currently in execution; characterised in that mask memories (11(l)-11(m)) are provided with the same identification numbers as the virtual machines, each corresponding to any one of the different identification numbers; in that I/O interruption queues (25(l)-25(m)) are provided with the same identification numbers as the virtual machines, each corresponding to any one of the different identification numbers; in that an I/O start for the I/O device by the central processing unit can be carried out, accompanying the designation of the identification number to which the I/O device in question belongs; in that the channel processor can set an I/O interrupt request of the I/O device into the I/O interruption queue corresponding to the identification number in question when the I/O interrupt request occurs; and in that the central processing unit can enable the mask memory indicated by the identification number stored in the identification memory, thereby determining whether or not the interrupt of the I/O device in question is enabled. A system according to claim 1, characterised by subchannel word storage means (26), wherein when the I/O start for the I/O device takes place, the central processing unit (1) can store the identification number corresponding to the I/O device in question with other control information into the subchannel word storage means, and the channel processor (3) can indicate the I/O interruption queue corresponding to the I/O device in question according to the identification number stored in the subchannel word storage means when the I/O interrupt request occurs. A system according to claim 1 or claim 2, characterised in that the mask memories (11(l)-11(m)) and the identification memory (12) are constituted by registers respectively. A system according to claim 2, characterised in that the subchannel word storage means (26) is constituted by a register. A system according to any preceding claim, characterised in that each I/O interruption queue (25(l)-25(m)) comprises a plurality of queue elements. A system according to any preceding claim, characterised in that the virtual machines (VM₁-VM m ) are controlled by a virtual machine control program (27) respectively.

Inventors: KANEDA, SABURO, MURAKAMI, KAZUAKI
Applicants: FUJITSU LIMITED
Application year: 1986
Main classification: G06F13
IPC codes: G06F13, G06F9