Hello list,
I'm puzzled as to why my KVM guest has IO that is 20 times slower than
the KVM host:
m...@guest:~$ dd if=/dev/zero of=/tmp/bigfile count=10
10+0 records in
10+0 records out
5120 bytes (51 MB) copied, 8.36612 s, 6.1 MB/s
m...@guest:~$ df -h
Filesystem
On Mar 25, 2009, at 12:13 PM, Avi Kivity wrote:
Kurt Yoder wrote:
Hello list,
I'm puzzled as to why my KVM guest has IO that is 20 times slower
than the KVM host:
m...@guest:~$ dd if=/dev/zero of=/tmp/bigfile count=10
10+0 records in
10+0 records out
5120 bytes (51 MB
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
On Mar 25, 2009, at 12:54 PM, Avi Kivity wrote:
Kurt Yoder wrote:
I upped the memory on the VM to 1 GB and ran the same test. It
actually got *slower*:
m...@guest:~$ free
total used free sharedbuffers
cached
Mem: 1024224 131324 892900
On Mar 25, 2009, at 1:55 PM, Avi Kivity wrote:
Kurt Yoder wrote:
What do you mean about the cache? Is my test fundamentally flawed?
I *thought* I was testing write speed on the disk...
'dd', without further arguments, will write to the page cache and
let the kernel write the data back
Kurt Yoder wrote:
I see. I looked up another test: using hdparm -t. It doesn't show the
situation as quite so bad, but the guest is still a little over half
the speed of the host:
m...@host:~$ sudo hdparm -t /dev/mapper/HW_RAID-ROOT
/dev/mapper/HW_RAID-ROOT:
Timing buffered disk reads
Kurt Yoder wrote:
snip
m...@guest:~# vmstat 1
procs ---memory-- ---swap-- -io -system--
cpu
r b swpd free buff cache si sobibo in cs us sy id
wa
1 0 2616 686488 7756 20800400 234 103 0 1 99
0
1 0
sorry to keep replying to myself:
Kurt Yoder wrote:
snip
So clearly there is something odd going on with the first one. It looks
like it's CPU-bound, and this is throttling the IO?
slow guest cpu information:
processor : 0
vendor_id : AuthenticAMD
cpu family : 6
model
On Mar 29, 2009, at 10:29 AM, Avi Kivity wrote:
Kurt Yoder wrote:
slow host cpu information, core 1 of 16:
processor : 0
vendor_id : AuthenticAMD
cpu family : 16
model : 4
model name : Quad-Core AMD Opteron(tm) Processor 8382
stepping: 2
cpu MHz
On Mar 29, 2009, at 10:29 AM, Avi Kivity wrote:
Kurt Yoder wrote:
snip
Can you loading kvm_amd on this host with 'modprobe kvm-amd npt=0'?
So that's most likely the problem for me:
m...@host:/etc/nagios/nrpe_directives$ sudo modprobe kvm-amd npt=0
FATAL: Error inserting kvm_amd (/lib
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