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Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspac
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends |
Date: |
Wed, 15 Jan 2014 10:54:43 +0200 |
On Tue, Jan 14, 2014 at 07:13:29PM +0100, Antonios Motakis wrote:
> Hello,
>
>
> On Tue, Jan 14, 2014 at 12:14 PM, Michael S. Tsirkin <address@hidden> wrote:
>
> On Mon, Jan 13, 2014 at 03:25:11PM +0100, Antonios Motakis wrote:
> > In this patch series we would like to introduce our approach for putting
> a
> > virtio-net backend in an external userspace process. Our eventual target
> is to
> > run the network backend in the Snabbswitch ethernet switch, while
> receiving
> > traffic from a guest inside QEMU/KVM which runs an unmodified virtio-net
> > implementation.
> >
> > For this, we are working into extending vhost to allow equivalent
> functionality
> > for userspace. Vhost already passes control of the data plane of
> virtio-net to
> > the host kernel; we want to realize a similar model, but for userspace.
> >
> > In this patch series the concept of a vhost-backend is introduced.
> >
> > We define two vhost backend types - vhost-kernel and vhost-user. The
> former is
> > the interface to the current kernel module implementation. Its control
> plane is
> > ioctl based. The data plane is the kernel directly accessing the QEMU
> allocated,
> > guest memory.
> >
> > In the new vhost-user backend, the control plane is based on
> communication
> > between QEMU and another userspace process using a unix domain socket.
> This
> > allows to implement a virtio backend for a guest running in QEMU, inside
> the
> > other userspace process.
> >
> > We change -mem-path to QemuOpts and add prealloc, share and unlink as
> properties
> > to it. HugeTLBFS requirements of -mem-path are relaxed, so any valid
> path
> can
> > be used now.
>
> Wait a second. This does not actually work well: if you mmap
> a random file outside HugeTLBFS, kernel won't create huge pages
> from this memory so performance of the system as a whole will suffer.
>
> You'll have fix the kernel MM before this scheme can fly.
>
>
> I'm not sure I completely understand this point. It is up to the user to
> choose
> not to use HugeTLBFS. Is there a particular problem with the kernel when not
> using it?
>
Yes. Linux supports transparent huge pages.
A bunch of anonymous pages are recombined into a single huge page,
all this without the drawbacks of HugeTLBFS and with no need for
special priveledges.
This is activated by default for qemu, by this line:
qemu_madvise(new_block->host, size, QEMU_MADV_HUGEPAGE);
this does not have effect for named pages which you get
if you mmap a file from a filesystem, so performance
goes down (unless you use HugeTLBFS but that needs special priveledges).
A different -mem-path having that effect is undesirable and unexpected.
>
>
> > The new properties allow more fine grained control over the guest
> > RAM backing store.
> >
> > The data path is realized by directly accessing the vrings and the
> buffer
> data
> > off the guest's memory.
> >
> > The current user of vhost-user is only vhost-net. We add new netdev
> backend
> > that is intended to initialize vhost-net with vhost-user backend.
> >
> > Example usage:
> >
> > qemu -m 1024 -mem-path /hugetlbfs,prealloc=on,share=on \
> > -netdev type=vhost-user,id=net0,path=/path/to/sock,poll_time=2500 \
> > -device virtio-net-pci,netdev=net0
> >
> > Changes from v5:
> > - Split -mem-path unlink option to a separate patch
> > - Fds are passed only in the ancillary data
> > - Stricter message size checks on receive/send
> > - Netdev vhost-user now includes path and poll_time options
> > - The connection probing interval is configurable
> >
> > Changes from v4:
> > - Use error_report for errors
> > - VhostUserMsg has new field `size` indicating the following payload
> length.
> > Field `flags` now has version and reply bits. The structure is
> packed.
> > - Send data is of variable length (`size` field in message)
> > - Receive in 2 steps, header and payload
> > - Add new message type VHOST_USER_ECHO, to check connection status
> >
> > Changes from v3:
> > - Convert -mem-path to QemuOpts with prealloc, share and unlink
> properties
> > - Set 1 sec timeout when read/write to the unix domain socket
> > - Fix file descriptor leak
> >
> > Changes from v2:
> > - Reconnect when the backend disappears
> >
> > Changes from v1:
> > - Implementation of vhost-user netdev backend
> > - Code improvements
> >
> > Antonios Motakis (8):
> > Convert -mem-path to QemuOpts and add prealloc and share properties
> > New -mem-path option - unlink.
> > Decouple vhost from kernel interface
> > Add vhost-user skeleton
> > Add domain socket communication for vhost-user backend
> > Add vhost-user calls implementation
> > Add new vhost-user netdev backend
> > Add vhost-user reconnection
> >
> > exec.c | 57 +++-
> > hmp-commands.hx | 4 +-
> > hw/net/vhost_net.c | 144 +++++++---
> > hw/net/virtio-net.c | 42 ++-
> > hw/scsi/vhost-scsi.c | 13 +-
> > hw/virtio/Makefile.objs | 2 +-
> > hw/virtio/vhost-backend.c | 556
> ++++++++++++++++++++++++++++++++++++++
> > hw/virtio/vhost.c | 46 ++--
> > include/exec/cpu-all.h | 3 -
> > include/hw/virtio/vhost-backend.h | 40 +++
> > include/hw/virtio/vhost.h | 4 +-
> > include/net/vhost-user.h | 17 ++
> > include/net/vhost_net.h | 15 +-
> > net/Makefile.objs | 2 +-
> > net/clients.h | 3 +
> > net/hub.c | 1 +
> > net/net.c | 2 +
> > net/tap.c | 16 +-
> > net/vhost-user.c | 177 ++++++++++++
> > qapi-schema.json | 21 +-
> > qemu-options.hx | 24 +-
> > vl.c | 41 ++-
> > 22 files changed, 1106 insertions(+), 124 deletions(-)
> > create mode 100644 hw/virtio/vhost-backend.c
> > create mode 100644 include/hw/virtio/vhost-backend.h
> > create mode 100644 include/net/vhost-user.h
> > create mode 100644 net/vhost-user.c
> >
> > --
> > 1.8.3.2
> >
>
>
- Re: [Qemu-devel] [PATCH v6 5/8] Add domain socket communication for vhost-user backend, (continued)
[Qemu-devel] [PATCH v6 7/8] Add new vhost-user netdev backend, Antonios Motakis, 2014/01/13
[Qemu-devel] [PATCH v6 8/8] Add vhost-user reconnection, Antonios Motakis, 2014/01/13
Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Michael S. Tsirkin, 2014/01/14
Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Michael S. Tsirkin, 2014/01/14
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Antonios Motakis, 2014/01/14
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Michael S. Tsirkin, 2014/01/15
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Antonios Motakis, 2014/01/15
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Michael S. Tsirkin, 2014/01/15
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Antonios Motakis, 2014/01/16
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Antonios Motakis, 2014/01/27
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Michael S. Tsirkin, 2014/01/27
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Antonios Motakis, 2014/01/29
- Re: [Qemu-devel] [PATCH v6 0/8] Vhost and vhost-net support for userspace based backends, Michael S. Tsirkin, 2014/01/29