Transcription of Mechanism: Limited Direct Execution
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Mechanism: Limited Direct Execution
6 Mechanism: Limited Direct ExecutionIn order to virtualize the CPU, the operating system needs to somehowshare the physical CPU among many jobs running seemingly at thesametime. The basic idea is simple: run one process for a little while, thenrun another one, and so forth. Bytime sharingthe CPU in this manner,virtualization is are a few challenges, however, in building such virtualizationmachinery. The first isperformance: how can we implement virtualiza-tion without adding excessive overhead to the system? The secondiscontrol: how can we run processes efficiently while retaining control overthe CPU? Control is particularly important to the OS, as it is in charge ofresources; without control, a process could simply run forever and takeover the machine, or access information that it should not be allowedtoaccess. Obtaining high performance while maintaining controlis thusone of the central challenges in building an operating :HOWTOEFFICIENTLYVIRTUALIZETHECPU WITHCONTROLThe OS must virtualize the CPU in an efficient manner while retainingcontrol over the system.
MECHANISM: LIMITED DIRECT EXECUTION 3 ASIDE: WHY SYSTEM CALLS LOOK LIKE PROCEDURE CALLS You may wonder why a call to a system call, such as open()or read(), looks exactly like a typical procedure call in C; that is, if it looks just like a procedure call, how does the system know it’s a system call, and do all
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