3/29/2023 0 Comments Indirection virtualization![]() ![]() So it can be done.īut until very recently, it could not be readily done with PCI and PCIe (PCI Express) IO. A virtual machine can issue an IO operation, have it directed to its address for an IO device (which may not be the "real" address), get the operation performed, and receive a completion interrupt, or an error, all without involving a hypervisor, at full hardware efficiency. And, of course, it is strongly supported in yet more hardware. One reason for all this mainframe talk is that it provides an existence proof: Mainframes have been virtualizing IO basically forever, allowing different virtual machines to think they completely own their own IO devices when in fact they're shared. Yet.Īs Moore's Law keeps providing us with more and more transistors, perhaps at some point the industry will tire of providing even more cores, and spend some of those transistors on something that might actually be immediately usable. ![]() Nobody else is willing to invest a pound or so of silicon into doing this. Not everything is as trivial as adding an offset, of course what happens with the memory mapping gets, to me anyway, a tad scary in its complexity. This implies that the bag 'o bits I've been glibly referring to becomes part of the hardware architecture: Now it's hardware that has to reach in and know where the clock offset resides. They embedded nearly the whole shooting match directly into silicon. It is perfectly possible to build hardware that adds an offset all by itself, without any "help" from software. All that has to happen is that a silly little offset is added. It is used, but in many cases another technique is used, alone or in combination with paravirtualization.Ĭonsider the example of reading the real time clock. In the previous discussion I might have lead you to believe that paravirtualization is widely used in mainframes (IBM zSeries and clones). To catch up, see Part 1, Part 2, and Part 3. This is the last part of a multi-part series that attempts to provide an approachable explanation of hardware virtualization. Pfister is the author of "In Search of Clusters," and over his 30-year career, he has accrued over 30 patents in parallel computing and computer communications. In the previous discussion I might have lead you to believe that paravirtualization is widely used in mainframes (IBM zSeries and clonīY GREG PFISTER Since retiring from his position as an IBM Distinguished Engineer, Greg Pfister has worked as an independent consultant as well as serving as research faculty at Colorado State University. ![]() Nonetheless, there remains a great deal of confusion regarding this increasingly popular technology. It is possible to find many explanations of hardware virtualization on the Internet and, of course, in computer science courses. Pfister is the author of “In Search of Clusters,” and over his 30-year career, he has accrued over 30 patents in parallel computing and computer communications. Feature - Back to Basics - How hardware virtualization works: Part 4īack to Basics - How hardware virtualization works: Part 4īY GREG PFISTER Since retiring from his position as an IBM Distinguished Engineer, Greg Pfister has worked as an independent consultant as well as serving as research faculty at Colorado State University. ![]()
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