On Mar 25, 2009, at 12:35 PM, Avi Kivity wrote:
Kurt Yoder wrote:
I get 141 MB/s on the same test (it only copies to memory
anyway). Is your VM under memory pressure?
I don't think so. The host has 128 GB of memory, and even the pre-
emptive kernel caching doesn't come close to filling it:
me@host:~$ free
total used free shared buffers
cached
Mem: 132043960 1742480 130301480 0 84628
826040
-/+ buffers/cache: 831812 131212148
Swap: 1048568 0 1048568
My /tmp should be physical disk in both cases. To be thorough, I
also ran the test while writing the output file to /, and got the
same results (5.7 MB/s on guest, 144 MB/s on host).
Your guest is only assigned 256MB though.
I upped the memory on the VM to 1 GB and ran the same test. It
actually got *slower*:
me@guest:~$ free
total used free shared buffers
cached
Mem: 1024224 131324 892900 0 1816
18328
-/+ buffers/cache: 111180 913044
Swap: 488248 0 488248
me@guest:~$ sudo -s
me@guest:~# dd if=/dev/zero of=/bigfile count=100000
100000+0 records in
100000+0 records out
51200000 bytes (51 MB) copied, 22.2141 s, 2.3 MB/s
I ran this three times to make sure it wasn't a fluke, and got those
same rates each time. The guest is now running thus:
root 19915 1 0 Mar24 ? 00:00:00 /usr/sbin/libvirtd -d
nobody 19937 19915 0 Mar24 ? 00:00:00 dnsmasq --keep-in-
foreground --strict-order --bind-interfaces --pid-file --conf-file --
listen-address 192.168.122.1 --except-interface lo --dhcp-leasefile=/
var/lib/libvirt/dhcp-default.leases --dhcp-range
192.168.122.2,192.168.122.254
root 25051 19915 54 12:40 ? 00:05:05 /usr/bin/kvm -S -M
pc -m 1024 -smp 1 -name guest -monitor pty -boot c -drive file=/dev/
HW_RAID/Guest,if=virtio,index=0,boot=on -net
nic,macaddr=52:54:00:ba:e6:db,vlan=0,model=virtio -net
tap,fd=11,script=,vlan=0,ifname=vnet1 -serial none -parallel none -usb
-vnc 127.0.0.1:1
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