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We ran a few experiments to compare performance of VMware's paravirtualization technique (VMI) and hardware MMU technologies (HWMMU) on VMware's hypervisor.
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Please note that specjbb is the worst case benchmark for hwmmu, due to the higher TLB miss latency, so it's a good result that the worst case benchmark has a degradation of only 1%.
VMware expects that these hardware virtualization features will be ubiquitous by 2011.
Apart from the performance benefit, VMI was important for Linux on VMware's platform, from timekeeping point of view, but with the tickless kernels and TSC improvements that were done for the mainline tree, we think VMI has outlived those requirements too.
In light of these results and availability of such hardware, we have decided to stop supporting VMI in our future products.
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vSphere4 monitor modes
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VMWARE WHITE PAPER
Table 1: Default monitor modes on Intel processors
Virtual Machine Con!guration
Core i7 45nm Core2 with VT-x
65nm Core2 with VT-x and
FlexPriority
65nm Core2 with VT-x
and No FlexPriority
P4 with VT-x EM64T without VT-x
No EM64T
FT enabled VT-x + swMMU
VT-x + swMMU VT-x + swMMU VT-x + swMMU Not Runnable Not Runnable Not Runnable
(*) When BT is used on an Intel system with VT-x capability, it dynamically switches to VT-x if the guest enters long mode.
(**) In VMI, para-virtualization is used for CPU and MMU virtualization. The guest kernel is statically modi!ed to make hyper-calls into the VMM to execute privileged instructions and perform page table updates [5].
Table 2: Intel processor technology and common server processors
Processor technology (from some columns of Table 1) Server processors
Core i7 Intel Xeon 5500 series
45nm Core 2 with VT-x Intel Xeon 5400 series
Intel Xeon 7400 series
65nm Core 2 with VT-x and FlexPriority Intel Xeon 7300 series
65nm Core 2 with VT-x and No FlexPriority Intel Xeon 5300 series