之前 QEMU 最多可支持 32 个 PCI 插槽。Red Hat Enterprise Linux 7.0 采用 PCI 桥接技术，可让用户配置 32 个以上的 PCI 设备。注：不支持桥接后的设备热插拔。
?QEMU 沙箱
Red Hat Enterprise Linux 7.0 使用内核系统调用过滤加强 KVM 虚拟化安全性，这提高了主机系统与虚拟机之间的独立性。
?支持 QEMU 虚拟 CPU 热添加
Red Hat Enterprise Linux 7.0 中的 QEMU 提供虚拟
CPU（vCPU）热添加支持。可在运行的虚拟机中添加虚拟
CPU（vCPUS）以满足与负载关联的负载要求或者保持服务等级协议（SLA）。注：只在使用 pc-i440fx-rhel7.0.0
机器类型的虚拟机中支持 vCPU 热插拔，这是 Red Hat Enterprise Linux 7.0 中的默认机器类型。
?多队列 NIC
多队列 virtio_net 提供更好的可延伸性。每个虚拟 CPU 都有独立的传输或者接收队列以及可在不影响其他虚拟 CPU 的情况下使用的独立中断。
?多队列 virtio_scsi
多队列 virtio_net 提供更好的可延伸性。每个虚拟 CPU 都有独立的队列以及可在不影响其他虚拟 CPU 的情况下使用的独立中断。
Q35 机型需要 KVM 虚拟机中的 PCI 快速总线支持，它是作为技术预览在 Red Hat Enterprise Linux 7.0 中提供。包含 AHCI 总线也只能在 Q35 机型中使用，同样也是技术预览。
?基于 VFIO 的 PCI 设备分配
虚拟功能 I/O（VFIO）用户空间驱动程序界面为 KVM 虚拟机提供改进的 PCI 设备分配解决方案。VFIO
提供内核级设备分离强化，提高设备访问的安全性，并与安全引导等功能兼容。VFIO 替换了 Red Hat Enterprise Linux 6
中使用的 KVM 设备分配机制。
?Intel VT-d 大页面
在 Red Hat Enterprise Linux 7.0 的 KVM 虚拟机中使用虚拟功能 I/O（VFIO）设备分配时，使用 2MB
页面作为输入/输出内存管理单位（IOMMU），因此可减少 I/O 操作的转译后备缓存（translation lookaside buffer
，TLB）的消耗。计划在 Red Hat Enterprise Linux 7.0 中提供 1GB 页面支持。VT-d
大页面功能支持目前仅限于 Intel 的平台。
?KVM 时钟获取时间性能
在 Red Hat Enterprise Linux 7.0 中加强了 vsyscall 机制以支持 KVM
虚拟机更迅速地从用户控件读取时钟。Red Hat Enterprise Linux 7.0 主机中运行的 Red Hat Enterprise
Linux 7.0 虚拟机可体验到经常读取时间的应用程序的性能提高。
?图像格式的 QCOW2 版本 3
Red Hat Enterprise Linux 7.0 添加对图像格式的 QCOW2 版本 3 的支持
?改进的实时迁移统计
现在可使用实时迁移的有关信息分析和调试性能。改进的统计包括预期关机、关机或者脏页面比例。
?实时迁移线程
已将 KVM 实时迁移功能改进为支持线程处理。
?字符设备和串行端口的热插拔
目前 Red Hat Enterprise Linux 7.0 支持为新字符设备热插拔新串行端口。
?模拟 AMD Opteron G5
KVM 现在可以模拟 AMD Opteron G5 处理器。
?在 KVM 虚拟机中支持新的 Intel 指令
KVM 虚拟机可以使用 Intel 22nm 处理器支持的新指令。这些包括：
浮点乘加器，
256 位整数向量，
大端移动指令（MOVBE）支持，
或者 HLE/HLE+。
?VPC 和 VHDX 文件格式
Red Hat Enterprise Linux 7.0 中的 KVM 包括对微软虚拟 PC（VPC）和微软 Hyper-V 虚拟硬盘（VHDX）文件格式的支持。
?libguestfs 新功能
libguestfs 是一组访问和修改虚拟机磁盘映像的工具。Red Hat Enterprise Linux 7.0 中的libguestfs 包括大量改进，最主要的包括：
使用 SELinux 或者 sVirt 包含的安全虚拟化，保证加强针对恶意和畸形磁盘映像的安全性。
可检查和修改远程磁盘，最开始是使用网络块设备（NBD）。
在某些程序中可进行磁盘热插拔以便获得更好的性能。
?WHQL 认证的 virtio-win 驱动程序
Red Hat Enterprise Linux 7.0 包括用于最新微软 Windows 虚拟机，即 Microsoft Window
8, 8.1, 2012 和 2012 R2 的 Windows 硬件质量实验室（WHQL）认证的 virtio-win 驱动程序。
--
Host and Guest Panic Notification in KVM
A new pvpanic virtual device can be
wired into the virtualization stack such that a guest panic can cause
libvirt to send a notification event to management applications.
pvpanic 设备可以添加到虚拟机，如果 guest panic 会触发libvirt发送通知给管理程序。
As opposed to the kdump mechanism, pvpanic does not need to reserve
memory in the guest kernel. It is not needed to install any dependency
packages in the guest. Also, the dumping procedure of pvpanic is
host-controlled, therefore the guest only cooperates to a minimal
extent.
To configure the panic mechanism, place the following snippet into the Domain XML devices element, by running virsh edit to open and edit the XML file:
After specifying the following snippet, the crashed domain's core
will be dumped. If the domain is restarted, it will use the same
configuration settings.
coredump-destroy
Power Management
Red Hat Enterprise Linux 7.0 provides a virtual power management
capability to suspend and resume a virtual machine. Both ACPI S3
(Suspend-to-RAM) and S4 (Suspend-to-Disk) power states can be advertised
to virtual machines using this capability. Enhancements are also made
to the kernel to ensure Red Hat Enterprise Linux used as a guest
suspends and resumes properly. This functionality is available in
Red Hat Enterprise Linux 7.0 as a Technology Preview.
通过虚拟电源管理 支持挂起和恢复虚拟机。
/*****************************************************下面是英文部分***************************************************************************/
?Improved Block I/O Performance Using virtio-blk-data-plane
In Red Hat Enterprise Linux 7, the virtio-blk-data-plane I/O virtualization functionality is available as a Technology Preview.
This functionality extends QEMU to perform disk I/O in a dedicated
thread that is optimized for I/O performance.
块设备IO使用virtio
PCI Bridge
QEMU previously supported only up to 32 PCI slots. Red Hat
Enterprise Linux 7 features PCI Bridge as a Technology Preview. This
functionality allows users to configure more than 32 PCI devices. Note
that hot plugging of devices behind the bridge is not supported.
允许链接超过32个pci设备，不允许热插拔
QEMU Sandboxing
Red Hat Enterprise Linux 7 features enhanced KVM virtualization
security through the use of kernel system call filtering, which improves
isolation between the host system and the guest.
增强虚拟化安全，通过使用kernel 系统调用过滤，增强主机和guest的独立性
QEMU Virtual CPU Hot Add Support
QEMU in Red Hat Enterprise Linux 7 features virtual CPU (vCPU) hot
add support. Virtual CPUs (vCPUs) can be added to a running virtual
machine in order to meet either the workload's demands or to maintain
the Service Level Agreement (SLA) associated with the workload. Note
that vCPU hot plug is only supported on virtual machines using the pc-i440fx-rhel7.0.0 machine type, the default machine type on Red Hat Enterprise Linux 7.
支持cpu特插拔
Multiple Queue NICs
Multiple queue virtio_net provides better scalability; each virtual
CPU can have a separate transmit or receive queue and separate
interrupts that it can use without influencing other virtual CPUs. Note
that this feature is only supported on Linux guests.
virtio_net 支持多队列，每个cpu有分离的收发队列，独立的中断，不影响其他虚拟cpu。只有linux guests可用该特性
Multiple Queue virtio_scsi
Multiple queue virtio_scsi provides better scalability; each virtual
CPU can have a separate queue and interrupts that it can use without
influencing other virtual CPUs. Note that this feature is only supported
on Linux guests.
多队列virtio_scsi，特性同virtio_net。只有linux guests可用该特性
Page Delta Compression for Live Migration
The KVM live migration feature has been improved by compressing the
guest memory pages and reducing the size of the transferred migration
data. This feature allows the migration to converge faster.
改进 kvm动态迁移，通过压缩guest os的内存页，降低了传输的数据量。该特性允许快速聚合迁移。
HyperV Enlightenment in KVM
KVM has been updated with several Microsoft Hyper-V functions; for
example, support for Memory Management Unit (MMU) and Virtual Interrupt
Controller. Microsoft provides a para-virtualized API between the guest
and the host, and by implementing parts of this functionality on the
host, and exposing it according to Microsoft specifications, Microsoft
Windows guests can improve their performance. Note that these functions
are not enabled by default.
kvm 增加了部分?HyperV 功能，例如，支持mmu 和虚拟终端控制器。微软在host和guest之间提供了并行虚拟API，通过在主机执行部分功能，windows的guests可以提升性能，这些功能过去并不支持。
EOI Acceleration for High Bandwidth I/O
Red Hat Enterprise Linux 7 utilizes Intel and AMD enhancements to
Advanced Programmable Interrupt Controller (APIC) to accelerate end of
interrupt (EOI) processing. For older chipsets, Red Hat
Enterprise Linux 7 provides para-virtualization options for EOI
acceleration.
……
USB 3.0 Support for KVM Guests
Red Hat Enterprise Linux 7 features improved USB support by adding
USB 3.0 host adapter (xHCI) emulation as a Technology Preview.
kvm guests 支持usb3.0
Microsoft Windows and Windows Server Guest Support
Red Hat Enterprise Linux 7 supports Microsoft Windows 8, Windows 8.1,
Windows Server 2012, and Windows Server 2012 R2 guests running inside
KVM virtual machines.
kvm支持运行Microsoft Windows 8, Windows 8.1,
Windows Server 2012,Windows Server 2012 R2
I/O Throttling for QEMU Guests
This feature provides I/O throttling, or limits, for QEMU guests'
block devices. I/O throttling slows down the processing of disk I/O
requests. This slows down one guest disk to reserve I/O bandwidth for
other tasks on host. Note that currently it is not possible to throttle
virtio-blk-data-plane devices.
IO限制，该功能可以缓慢硬盘IO请求。该功能可以限制guest的IO带宽。virtio-blk-data-plane目前不能使用该特性。
Integration of Ballooning and Transparent Huge Pages
Ballooning and transparent huge pages are better integrated in
Red Hat Enterprise Linux 7. Balloon pages can be moved and compacted so
they can become huge pages.
气球和透明大页
Pulling System Entropy from Host
A new device, virtio-rng, can be
configured for guests, which will make entropy available to guests from
the host. By default, this information is sourced from the host's /dev/random file, but hardware random number generators (RNGs) available on hosts can be used as the source as well.
新设备 virtio-rng 使用硬随机数
Bridge Zero Copy Transmit
Bridge zero-copy transmit is a performance feature to improve CPU
processing of large messages. The bridge zero-copy transmit feature
improves performance from guest to external traffic when using a bridge.
Note that this function is disabled by default.
桥，零copy传输特性，大数据量情况下可以提升cpu性能。
Live Migration Support
Live migration of a guest from a Red Hat Enterprise Linux 6.5 host to a Red Hat Enterprise Linux 7 host is supported.
支持从Red Hat6.5动态迁移到Red Hat7
Discard Support in qemu-kvm
Discard support, using the fstrim or mount -o discard command, works on a guest after adding discard='unmap' to the element in the domain's XML definition. For example:
qemu支持discard特性
...
NVIDIA GPU Device Assignment
Red Hat Enterprise Linux 7 supports device assignment of NVIDIA
professional series graphics devices (GRID and Quadro) as a secondary
graphics device to emulated VGA.
支持将 NVIDIA 显卡(GRID and Quadro)作为 仿真vga的2级显示设备？？？--不明白是什么意思
Para-Virtualized Ticketlocks
Red Hat Enterprise Linux 7 supports para-virtualized ticketlocks
(pvticketlocks) that improve performance of Red Hat Enterprise Linux 7
guest virtual machines running over Red Hat Enterprise Linux 7 hosts
with oversubscribed CPUs.
Error Handling on Assigned PCIe Devices
If a PCIe device with Advanced Error Reporting (AER) encounters an
error while assigned to a guest, the affected guest is brought down
without impacting any other running guests or the host. The guests can
be brought back up after the host driver for the device recovers from
the error.
Q35 Chipset, PCI Express Bus and AHCI Bus Emulation
The Q35 machine type, required for PCI express bus support in KVM
guest virtual machines, is available as a Technology Preview in Red Hat
Enterprise Linux 7. An AHCI bus is only supported for inclusion with the
Q35 machine type and is also available as a Technology Preview Red Hat
Enterprise Linux 7.
VFIO-based PCI Device Assignment
The Virtual Function I/O (VFIO) user-space driver interface provides
KVM guest virtual machines with an improved PCI device assignment
solution. VFIO provides kernel-level enforcement of device isolation,
improves security of device access and is compatible with features such
as secure boot. VFIO replaces the KVM device assignment mechanism used
in Red Hat Enterprise Linux 6.
Intel VT-d Large Pages
When using Virtual Function I/O (VFIO) device assignment with a KVM
guest virtual machine on Red Hat Enterprise Linux 7, 1GB pages are used
by the input/output memory management unit (IOMMU), thus reducing
translation lookaside buffer (TLB) overhead for I/O operations. 2MB and
1GB page sizes are supported. The VT-d large pages feature is only
supported on certain more recent Intel-based platforms.
KVM Clock Get Time Performance
In Red Hat Enterprise Linux 7 the vsyscall mechanism was enhanced to support fast reads of the clock from the user
space for KVM guests. A guest virtual machine running Red Hat
Enterprise Linux 7 on a Red Hat Enterprise Linux 7 host will see
improved performance for applications that read the time of day
frequently.
QCOW2 Version 3 Image Format
Red Hat Enterprise Linux 7 adds support for the QCOW2 version 3 Image Format.
Improved Live Migration Statistics
Information about live migration is now available to analyze and tune
performance. Improved statistics include: total time, expected
downtime, and bandwidth being used.
Live Migration Thread
The KVM live migration feature now uses its own thread. As a result,
the guest performance is virtually not impacted by migration.
Hot Plugging of Character Devices and Serial Ports
Hot plugging new serial ports with new character devices is now supported in Red Hat Enterprise Linux 7.
Emulation of AMD Opteron G5
KVM is now able to emulate AMD Opteron G5 processors.
Support of New Intel Instructions on KVM Guests
KVM guests can use new instructions supported by Intel 22nm processors. These include:
Floating-Point Fused Multiply-Add;
256-bit Integer vectors;
big-endian move instruction (MOVBE) support;
or HLE/HLE+.
VPC and VHDX File Formats
KVM in Red Hat Enterprise Linux 7 includes support for the Microsoft
Virtual PC (VPC) and Microsoft Hyper-V virtual hard disk (VHDX) file
formats. Note that these formats are supported in read-only mode only.
New Features in libguestfs
libguestfs is a set of tools for accessing and modifying virtual machine disk images. libguestfs included in Red Hat Enterprise Linux 7 includes a number of improvements, the most notable of which are the following:
Secure Virtualization Using SELinux, or sVirt protection, ensures
enhanced security against malicious and malformed disk images.
Remote disks can be examined and modified, initially over Network Block Device (NBD).
Disks can be hot plugged for better performance in certain applications.
WHQL-Certified virtio-win Drivers
Red Hat Enterprise Linux 7 includes Windows Hardware Quality Labs (WHQL) certified virtio-win drivers for the latest Microsoft Windows guests, namely Microsoft Windows 8, 8.1, 2012 and 2012 R2.
Host and Guest Panic Notification in KVM
A new pvpanic virtual device can be
wired into the virtualization stack such that a guest panic can cause
libvirt to send a notification event to management applications.
pvpanic 设备可以添加到虚拟机，如果 guest panic 会触发libvirt发送通知给管理程序。
As opposed to the kdump mechanism, pvpanic does not need to reserve
memory in the guest kernel. It is not needed to install any dependency
packages in the guest. Also, the dumping procedure of pvpanic is
host-controlled, therefore the guest only cooperates to a minimal
extent.
To configure the panic mechanism, place the following snippet into the Domain XML devices element, by running virsh edit to open and edit the XML file:
After specifying the following snippet, the crashed domain's core
will be dumped. If the domain is restarted, it will use the same
configuration settings.
coredump-destroy
Power Management
Red Hat Enterprise Linux 7.0 provides a virtual power management
capability to suspend and resume a virtual machine. Both ACPI S3
(Suspend-to-RAM) and S4 (Suspend-to-Disk) power states can be advertised
to virtual machines using this capability. Enhancements are also made
to the kernel to ensure Red Hat Enterprise Linux used as a guest
suspends and resumes properly. This functionality is available in
Red Hat Enterprise Linux 7.0 as a Technology Preview.
通过虚拟电源管理 支持挂起和恢复虚拟机。
