Methods for Consistency of Channel-Path-Reconnection with Direct I/O-Execution

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概要

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• Methods are presented for the consistency of the Channel-Path-Reconnection (CPR) with the Direct I/O-Execution (DIO). The CPR is the native function of the channel subsystem, and dynamically reconnects devices to free channel-paths at ends of I/O operations. The CPR is effective in a channel-path-group, which is a set of channel-paths, and defined by an OS to use it. The CPR is the key function to enhance I/O response. On the other hand, the DIO means that real host computers directly execute the I/O instructions and I/O interrupts of virtual machines (VMs) without intervention of a virtual machine monitor (VMM), which is a control program for controlling the VMs. The DIO is the key feature to improve VM CPU performance. Conventionally, in shared channel-paths by the VMs, guest OSs(i.e., OSs in VMs) cannot use the CPR and the DIO at the same time. This restriction comes from uniqueness requirement of a channel-path : A channel-path with the CPR has to belong to only one channel-path-group. This requirement is reasonable in real machine environment. In VM environment, multiple guest OSs are going to define their own channel-path-groups that contain shared channel-paths. The definitions do not satisfy the above-stated uniqueness requirement. Therefore, they are rejected and the guest OSs cannot use the CPR to the shared channel-paths, though they can use the DIO for other I/O instructions. The proposed methods consist of handshakings, which mean modifying OSs for VMs, and several hardware extensions for channel-path-groups and channel-path modes. Channel-path-groups are recognized by their identifiers. In the handshakings, the VMM gives the OSs channel-path-group identifiers that satisfy the uniqueness requirement of channel-paths based on the forms of channel-path allocation. One of the hardware extensions eases the uniqueness requirement of channel-paths, that is, the uniqueness is required only in guest OSs, and not in a total system. The extension enables the guest OSs to compose their own channel-path-groups that contain shared channel-paths under the DIO. Any one of the proposed methods can provide consistency of the CPR with the DIO to the VMs whether channel-paths are shared by the VMs or not.

• 一般社団法人情報処理学会の論文
• 1995-05-15

著者

• Inoue Taro

  Department 3 Systems Development Laboratory Hitachi Ltd.

• Umeno Hidenori

  Software Development Department General Purpose Computer Division Hitachi Ltd.

• Tanaka Shunji

  Department 3 Systems Development Laboratory Hitachi Ltd.

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