3a4d5c94e9
What it is: vhost net is a character device that can be used to reduce the number of system calls involved in virtio networking. Existing virtio net code is used in the guest without modification. There's similarity with vringfd, with some differences and reduced scope - uses eventfd for signalling - structures can be moved around in memory at any time (good for migration, bug work-arounds in userspace) - write logging is supported (good for migration) - support memory table and not just an offset (needed for kvm) common virtio related code has been put in a separate file vhost.c and can be made into a separate module if/when more backends appear. I used Rusty's lguest.c as the source for developing this part : this supplied me with witty comments I wouldn't be able to write myself. What it is not: vhost net is not a bus, and not a generic new system call. No assumptions are made on how guest performs hypercalls. Userspace hypervisors are supported as well as kvm. How it works: Basically, we connect virtio frontend (configured by userspace) to a backend. The backend could be a network device, or a tap device. Backend is also configured by userspace, including vlan/mac etc. Status: This works for me, and I haven't see any crashes. Compared to userspace, people reported improved latency (as I save up to 4 system calls per packet), as well as better bandwidth and CPU utilization. Features that I plan to look at in the future: - mergeable buffers - zero copy - scalability tuning: figure out the best threading model to use Note on RCU usage (this is also documented in vhost.h, near private_pointer which is the value protected by this variant of RCU): what is happening is that the rcu_dereference() is being used in a workqueue item. The role of rcu_read_lock() is taken on by the start of execution of the workqueue item, of rcu_read_unlock() by the end of execution of the workqueue item, and of synchronize_rcu() by flush_workqueue()/flush_work(). In the future we might need to apply some gcc attribute or sparse annotation to the function passed to INIT_WORK(). Paul's ack below is for this RCU usage. (Includes fixes by Alan Cox <alan@linux.intel.com>, David L Stevens <dlstevens@us.ibm.com>, Chris Wright <chrisw@redhat.com>) Acked-by: Rusty Russell <rusty@rustcorp.com.au> Acked-by: Arnd Bergmann <arnd@arndb.de> Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
72 lines
1.9 KiB
Text
72 lines
1.9 KiB
Text
#
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# KVM configuration
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#
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source "virt/kvm/Kconfig"
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menuconfig VIRTUALIZATION
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bool "Virtualization"
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depends on HAVE_KVM || X86
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default y
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---help---
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Say Y here to get to see options for using your Linux host to run other
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operating systems inside virtual machines (guests).
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This option alone does not add any kernel code.
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If you say N, all options in this submenu will be skipped and disabled.
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if VIRTUALIZATION
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config KVM
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tristate "Kernel-based Virtual Machine (KVM) support"
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depends on HAVE_KVM
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# for device assignment:
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depends on PCI
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select PREEMPT_NOTIFIERS
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select MMU_NOTIFIER
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select ANON_INODES
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select HAVE_KVM_IRQCHIP
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select HAVE_KVM_EVENTFD
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select KVM_APIC_ARCHITECTURE
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select USER_RETURN_NOTIFIER
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---help---
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Support hosting fully virtualized guest machines using hardware
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virtualization extensions. You will need a fairly recent
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processor equipped with virtualization extensions. You will also
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need to select one or more of the processor modules below.
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This module provides access to the hardware capabilities through
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a character device node named /dev/kvm.
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To compile this as a module, choose M here: the module
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will be called kvm.
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If unsure, say N.
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config KVM_INTEL
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tristate "KVM for Intel processors support"
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depends on KVM
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---help---
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Provides support for KVM on Intel processors equipped with the VT
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extensions.
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To compile this as a module, choose M here: the module
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will be called kvm-intel.
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config KVM_AMD
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tristate "KVM for AMD processors support"
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depends on KVM
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---help---
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Provides support for KVM on AMD processors equipped with the AMD-V
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(SVM) extensions.
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To compile this as a module, choose M here: the module
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will be called kvm-amd.
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# OK, it's a little counter-intuitive to do this, but it puts it neatly under
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# the virtualization menu.
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source drivers/vhost/Kconfig
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source drivers/lguest/Kconfig
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source drivers/virtio/Kconfig
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endif # VIRTUALIZATION
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