From: Arjan Koers <0h61vkll2ly8@xutrox.com>
To: kvm@vger.kernel.org
Subject: vhost-net guest memory usage
Date: Mon, 27 Dec 2010 21:48:19 +0100 [thread overview]
Message-ID: <4D18FB93.8000105@xutrox.com> (raw)
When running my guests with 'vhost=on', a lot less guest memory is
available (about 18.5 MB less for each networking device).
I searched the mailing list archive and found a comment by Michael S.
Tsirkin:
"with vhost, virtio does currently consume a bit more memory than with
userspace backend"
Is 18.5 MB per device the expected amount, and can I change some
setting to reduce it?
Here's the 'free' output of a guest with 7 tap devices (qemu-kvm 0.13.0,
linux 2.6.36.2 host and guest):
Started the guest with 'vhost=off':
total used free shared buffers cached
Mem: 253564 39260 214304 0 1732 15124
-/+ buffers/cache: 22404 231160
Swap: 409620 0 409620
Same guest, but with 'vhost=on':
total used free shared buffers cached
Mem: 253564 169092 84472 0 1744 15120
-/+ buffers/cache: 152228 101336
Swap: 409620 0 409620
The command that started the guest:
/opt/kvm/bin/qemu-system-x86_64 \
-nographic \
-daemonize \
-cpu host \
-M pc-0.13 \
-m 256 \
-mem-path /hugepages \
-smp 2 \
-name gw \
-uuid d9d6332d-10ba-4cfa-925b-4e4d14f7cd86 \
-boot c \
-drive file=/opt/kvm/var/img/gw.raw,if=virtio,index=0,boot=on,cache=none \
-device virtio-net-pci,netdev=virtio.0,mac=fe:60:20:3a:8d:37 \
-netdev tap,id=virtio.0,ifname=gw-lan,script=no,downscript=no,vhost=on \
-device virtio-net-pci,netdev=virtio.1,mac=06:c8:4d:85:47:45 \
-netdev tap,id=virtio.1,ifname=gw-dmz,script=no,downscript=no,vhost=on \
-device virtio-net-pci,netdev=virtio.2,mac=e2:57:e2:6b:67:7c \
-netdev tap,id=virtio.2,ifname=gw-inet,script=no,downscript=no,vhost=on \
-device virtio-net-pci,netdev=virtio.3,mac=72:47:f5:4d:59:01 \
-netdev tap,id=virtio.3,ifname=gw-lanv,script=no,downscript=no,vhost=on \
-device virtio-net-pci,netdev=virtio.4,mac=02:de:c4:7b:71:6e \
-netdev tap,id=virtio.4,ifname=gw-dmzv,script=no,downscript=no,vhost=on \
-device virtio-net-pci,netdev=virtio.5,mac=fe:6a:ac:4e:16:f3 \
-netdev tap,id=virtio.5,ifname=gw-lanvpn,script=no,downscript=no,vhost=on \
-device virtio-net-pci,netdev=virtio.6,mac=7e:33:75:7a:ec:cd \
-netdev tap,id=virtio.6,ifname=gw-dmzvpn,script=no,downscript=no,vhost=on \
-serial unix:/opt/kvm/var/run/gw-serial.socket,server,nowait \
-monitor unix:/opt/kvm/var/run/gw-monitor.socket,server,nowait \
-parallel none \
-vga cirrus \
-runas kvm-gw
reply other threads:[~2010-12-27 21:08 UTC|newest]
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