O'shantel Software L.l.c.

Other

Reliable Technologies, Inc.

Donald D Burn

Jack Justin Stiffler

System-directed checkpointing is enabled in otherwise standard computers through relatively straightforward augmentations to the computer's memory controller hub. Firmware routines executed by a control and dispatch unit that is normally part of any memory controller hub enable it to implement any of six different checkpointing strategies: post-image checkpointing in which an image of the system state at the time of the last checkpoint is maintained in a local shadow memory; post-image checkpointing in which an image of the system state at the time of the last checkpoint is maintained in a shadow memory located in a second, backup computer; post-image checkpointing using a bit-map memory, having one bit representing each data block in system memory, to reduce the amount of memory-to-memory copying required to establish a checkpoint; post-image checkpointing to a local shadow memory using two bit map memories to enable normal processing to continue while the shadow is being updated, post-image checkpointing to a local shadow memory using a block-state memory that eliminates the need for any memory-to-memory copying; and local pre-image checkpointing that does not require a shadow memory. Since each of these implementations has advantages and disadvantages relative to the others and since similar mechanisms are used in the memory controller hub for all of these options, it can be designed to support all of them with hardwired or settable status bits defining which is to be supported in a given situation.

Memory-controller-embedded apparatus and procedure for achieving system-directed checkpointing without operating-system kernel support

While system-directed checkpointing can be implemented in various ways, for example by adding checkpointing support in the memory controller or in the operating system in otherwise standard computers, implementation at the hypervisor level enables the necessary state information to be captured efficiently while providing a number of ancillary advantages over those prior-art methods. This disclosure details procedures for realizing those advantages through relatively minor modifications to normal hypervisor operations. Specifically, by capturing state information in a guest-operating-system-specific manner, any guest operating system can be rolled back independently and resumed without losing either program or input/output (I/O) continuity and without affecting the operation of the other operating systems or their associated applications supported by the same hypervisor. Similarly, by managing I/O queues as described herein, rollback can be accomplished without requiring I/O operations to be repeated and I/O device failures can be circumvented without losing any I/O data in the process.

System-directed checkpointing implementation using a hypervisor layer

While system-directed checkpointing can be implemented in various ways, for example by adding checkpointing support in the memory controller or in the operating system in otherwise standard computers, implementation at the hypervisor level enables the necessary state information to be captured efficiently while providing a number of ancillary advantages over those prior-art methods. This disclosure details procedures for realizing those advantages through relatively minor modifications to normal hypervisor operations. Specifically, by capturing state information in a guest-operating-system-specific manner, any guest operating system can be rolled back independently and resumed without losing either program or input/output (I/O) continuity and without affecting the operation of the other operating systems or their associated applications supported by the same hypervisor. Similarly, by managing I/O queues as described in this disclosure, rollback can be accomplished without requiring I/O operations to be repeated and I/O device failures can be circumvented without losing any I/O data in the process.

System-directed checkpointing is accomplished following each checkpoint by mapping all memory pages, including read-only pages and read/write pages as read-only pages. Therefore, when an attempt is made to write to a page, a page-fault interrupt is generated. If the page is a read-only page, then normal page-fault interrupt protocol is followed. If the page is a read/write page that has temporarily been labeled read-only, the page is copied to a buffer and the memory map is changed to indicate that the page is now a read/write page. The pages in the buffer can then be used to restore the system after a fault. In accordance with another embodiment of the invention, after the aforementioned system interrupt occurs, the identity of the page is recorded in a backup computer, but the page itself is not copied. In addition, the locations of all pages modified through I/O events are also recorded. At the time of a checkpoint, the checkpoint software copies the contents of all modified pages to a memory in the backup computer. The backup computer can then be used to restart the system after a fault. This latter technique can also be used in a clustered environment with one computer effectively serving as a backup for every other computer in the cluster.

Growing community of inventors

Westborough, MA, United States of America

Donald D Burn