Reduction of 2-0-Translation Table Maintenance Overhead in a Virtual Machine System

概要

論文の詳細を見る
Methods are presented to reduce CPU overhead when an Operating System(OS) with multiple virtual storage is running under a Virtual Machine System(VMS) with 2-0-translation tables, which are also called shadow tables and translate level 2 addresses (i.e. OS's virtual addresses) to level 0 addresses (i.e. system's real addresses). The conventional multiple 2-0-translation table method has the advantage that 2-0-translation tables can be used corresponding to each OS's virtual storage, and it reduces VMS's CPU overhead due to an OS switching its virtual storage. However, it has some disadvantages. That is, (1)an OS in a VM may issue a privileged instruction to invalidate pages during its paging process. In order to simulate it, the associated 2-0-translation table entries have to also be invalidated, which means to cancel the address mapping from level 2 page addresses to level 0 page addresses. This invalidation overhead will increase in proportion to the number of 2-0-translation tables. (2)Moreover, the switching of multiple 2-0-translation tables is a new additional CPU overhead. In order to solve the problem, an assist is invented to selectively invalidate the 2-0-translation table under the condition that a page address to be invalidated is given in a privileged instruction used for the OS's page invalidation process. Moreover, another assist is developed to realize fast 2-0-translation table switching corresponding to switching OS's virtual storage. These two assists are named, generically, Multi-Shadow Assist(MSA), which is applicable to any Virtual Machine(VM) irrespective of its memory attributes. Acceleration ratios of MSA to associated software processes are estimated at 3.4〜24.4. Multi-Shadow Assist is experimentally implemented in Hitachi's VMS using conventional hardware architecture, and performance measurements are obtained on some benchmark jobs for this report. Performance data which confirm the effectiveness of MSA are presented. Multi-Shadow Assist reduces almost all the 2-0-translation table maintenance overhead, with a 10% reduction in mean instruction execution time, and a 40%〜60% reduction in total CPU overhead. Moreover, a method to prevent the double invalidation of the 2-0-translation tables is proposed. It is effective for the temporary increase of the number of the OS's active virtual storage. This performance improvement efficiently supports the OS with multiple virtual storage running under the VMS using conventional hardware architecture.
一般社団法人情報処理学会の論文
1985-03-31

Reduction of 2-0-Translation Table Maintenance Overhead in a Virtual Machine System

スポンサーリンク

概要

著者

関連論文

スポンサーリンク