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Unformatted text preview: (on the order of tens of milliseconds), so instead of waiting and doing nothing in the interim, the kernel performs a context switch from process A to B. Note that before the switch, the kernel is executing instructions in user mode on behalf of process A. During the 402
Process A Time CHAPTER 8. EXCEPTIONAL CONTROL FLOW
Process B user code kernel code read() disk interrupt context switch context switch user code kernel code user code Figure 8.12: Anatomy of a context switch. ﬁrst part of the switch, the kernel is executing instructions in kernel mode on behalf of process A. Then at some point it begins executing instructions (still in kernel mode) on behalf of process B. And after the switch, the kernel is executing instructions in user mode on behalf of process B. Process B then runs for a while in user mode until the disk sends an interrupt to signal that data has been transferred from disk to memory. The kernel decides that process B has run long enough and performs a context switch from process B to A, returning cont...
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- Spring '10
- The American