Paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar but not identical to the underlying hardware. This requires the guest operating systems to be modified to use this special API rather than standard hardware interfaces.
The paravirtualized interface enables:
- Hypervisors to offer higher performance
- Access special hypervisor capabilities not available through normal hardware
- Avoid needing to emulate hardware, which enables major efficiency advantages
Key characteristics of paravirtualization include:
- Guest OSes must be modified to replace hardware calls with hypervisor API
- Hypervisor can be thinner, not needing hardware emulation
- Performance can be significantly improved
Paravirtualization provides major advantages over full virtualization, which completely simulates hardware without any guest modification. The tradeoff is the need to adapt guest operating systems.
Full virtualization vs paravirtualization
Full virtualization uses binary translation to allow unmodified OSes treating the VM as real hardware, but comes with CPU & memory overhead.
Paravirtualization reduces overhead via the guest OS-hypervisor integration, but requires modifying guest OS kernels.
Key differences include:
- Guest kernel modifications – Paravirtualization requires changes to replace hardware calls with hypervisor APIs, full virtualization does not
- Performance – Paravirtualization reduces CPU overhead for faster performance
- Hardware support – Full virtualization requires virtualization hardware extensions not needed in paravirtualization
Paravirtualization improves efficiency by avoiding the need to emulate hardware, providing higher utilization and scalability. But the guest modifications create compatibility limitations that full virtualization does not have.
Does VMware use paravirtualization?
VMware utilizes a mix of virtualization techniques, rather than a pure paravirtualized approach. Key methods include:
VMware uses binary translation to allow unmodified guest OSes to run without paravirtualization, like full virtualization. This enables broad hardware and OS support.
VMware also leverages OS-assisted virtualization for partially paravirtualized device drivers integrated with multiple guest OSes. This provides fast I/O performance without extensive kernel changes.
So while VMware virtualization includes some paravirtualized components, it is not fully paravirtualized, instead providing flexibility across the performance vs compatibility tradeoff spectrum.
VMware’s approach to improving efficiency
Rather than relying solely on paravirtualization, VMware uses a suite of technologies to reduce overhead, gain efficiencies, and improve scalability including:
Memory management optimization
- Page sharing to eliminate duplicate memory pages
- Transparent page sharing does not require guest involvement
- Compression further reduces memory overhead
- Adaptive page fault analysis to optimize context switching
- CPU scheduler load balancing for efficient multi-core usage
- Storage I/O control for managing large storage loads
- Paravirtualized disk and network drivers for fast I/O without full kernel changes
This combination of memory, CPU, I/O, and hypervisor efficiency gains provides significant utilization and scalability improvements without requiring full paravirtualization.
When to choose paravirtualization vs alternatives
Key factors driving virtualization approach choices include:
- OS support needs – Paravirtualization limits OS compatibility
- Performance needs – Paravirtualization improves efficiency over full virtualization
- Existing infrastructure – Upgrading OSes to support paravirtualization has downsides
For broad hardware and operating system support, full virtualization is often preferable.
For maximum density and scalability on supported guest OS platforms, paravirtualization delivers superior performance.
For flexibility across unsupported legacy OSes and cloud-native apps, VMware’s hybrid model maintains compatibility while improving efficiency.
There are tradeoffs between guest OS modification requirements, compatibility, and efficiency gains amongst virtualization options that drive technology choices for specific application needs.
- Paravirtualization improves performance but requires guest OS kernel changes
- VMware uses a mix of paravirtualized device drivers combined with binary translation
- This OS-assisted virtualization avoids full paravirtualization downsides
- VMware focuses on memory, CPU, storage optimizations rather than only paravirtualization
- Virtualization technique choices depend on OS support needs vs efficiency gains
While paravirtualization can provide significant performance advantages, its guest OS modification requirements create compatibility limitations. VMware virtualization leverages a blend of paravirtualized components along with binary translation and other optimization techniques as a compromise providing excellent support, efficiency, and scalability without fully paravirtualizing guests. This hybrid model balances the tradeoffs involved between hardware support, operating system compatibility needs, efficiency levels and overall virtualization goals.
Frequently Asked Questions
- What is paravirtualization?
Paravirtualization is a virtualization technique presenting a software interface similar but not identical to underlying hardware. It requires guest operating systems to be modified to use the special API rather than standard hardware interfaces.
- How does paravirtualization differ from full virtualization?
Paravirtualization provides higher performance by not needing hardware emulation, but requires guest OS changes. Full virtualization uses binary translation to emulate hardware without modifications but has higher CPU and memory overhead.
- Does VMware use paravirtualization?
VMware does not fully paravirtualize guests but rather uses a mix of paravirtualized device drivers and binary translation to balance tradeoffs between performance and compatibility.
- What techniques does VMware use to improve efficiency?
Rather than only paravirtualization, VMware uses memory management optimizations like page sharing, CPU scheduling improvements, paravirtualized disk and network drivers, and storage I/O control to drive efficiency gains across the hypervisor.
- When should paravirtualization be used vs alternatives?
Paravirtualization is best for new high density applications on supported guest OSes needing maximum efficiency. Full virtualization provides broader hardware and OS support. VMware’s hybrid model balances compatibility, support for legacy platforms, and improved performance.
- Does paravirtualization provide higher or lower performance than full virtualization?
Paravirtualization provides significantly higher performance by avoiding the need to emulate hardware. But it limits support to modified guest operating systems.
- What is binary translation?
Binary translation is a technique that allows unmodified guest OS binaries to run on virtual hardware without paravirtualization. This enables broader operating system support.
- What is OS-assisted virtualization?
OS-assisted virtualization refers to paravirtualized device drivers integrated into the guest OS kernel to provide fast I/O without needing the full OS to be paravirtualized. This improves performance for supported devices.
- What techniques does VMware use to optimize memory usage?
VMware utilizes memory page sharing to eliminate duplicate pages across VMs, transparent page sharing without guest involvement, and memory compression to reduce overhead.
- How does VMware optimize CPU utilization in its hypervisor?
VMware leverages adaptive page fault analysis to reduce context switching overhead as well as advanced CPU schedulers to load balance across cores and enable efficient simultaneous multi-threading.
- What storage optimization does VMware use?
For storage, VMware uses storage I/O control technology to efficiently manage large storage loads across heterogeneous arrays and PARAVIRTUALIZED disk/network drivers for maximum I/O throughput.
- When is paravirtualization the best virtualization choice?
Paravirtualization provides the highest scalability and density for supported guest operating systems when maximum efficiency on new high performing platforms is critical.
- When is full virtualization preferable to paravirtualization?
Full virtualization supports a far broader range of operating systems and hardware without any guest modification requirements, making it preferable for heterogeneous legacy environments.
- What causes the performance differences between full and paravirtualization?
By avoiding hardware emulation, paravirtualization reduces CPU overhead and memory costs significantly. Full virtualization’s binary translation has inherent but manageable translation overhead.
- What are the limitations of paravirtualization vs alternatives?
Paravirtualization guest kernel modification requirements limit supported operating systems. Additionally transitioning existing OS images can require significant effort.
- How does VMware balance paravirtualization pros and cons?
Rather than full paravirtualization, VMware uses it selectively for device drivers combined with binary translation across the hypervisor stack to balance performance and compatibility.