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authorMichael S. Tsirkin <mst@redhat.com>2010-01-14 06:17:27 +0000
committerDavid S. Miller <davem@davemloft.net>2010-01-15 01:43:29 -0800
commit3a4d5c94e959359ece6d6b55045c3f046677f55c (patch)
tree113cfe31540e3d77925837f6990c3284d425bfd1 /arch/s390/kvm
parent5da779c34ccff5e1e617892b6c8bd8260fb1f04c (diff)
downloadlinux-linaro-android-3a4d5c94e959359ece6d6b55045c3f046677f55c.tar.gz
vhost_net: a kernel-level virtio server
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>
Diffstat (limited to 'arch/s390/kvm')
-rw-r--r--arch/s390/kvm/Kconfig1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 6ee55ae84ce..a7251580891 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -35,6 +35,7 @@ config KVM
# OK, it's a little counter-intuitive to do this, but it puts it neatly under
# the virtualization menu.
+source drivers/vhost/Kconfig
source drivers/virtio/Kconfig
endif # VIRTUALIZATION