1:28 p.m.
Hi,
I have a fedora15 x86_64 host with one fedora15 guest running
amavis+spamassassin+postfix and performance is horrible. The host is a
quad-core E13240 with 16GB and 3 1TB Seagate ST31000524NS and all
partitions are ext4. I've allocated 4 processors and 8GB of RAM to
this guest. I really hoped someone could help me identify areas in
which performance can be improved at both the guest and host.
Load on the server is regularly above 20, yet the processors generally
are idle and the host is still responsive.
Should the concentration of the performance tuning be done on the
guest or the host? I've read through the information at
http://libvirt.org/formatdomain.html#elementsMemoryTuning but I don't
know how the settings apply to my configuration and which ones apply
to my hardware.
I've included my libvirt xml config below. It was built using
virt-manager on fedora15. There appears to be quite a few other
options that are available and not provided by virt-manager that I
would like to be able to use.
I've done a little kernel tuning on the host, although it doesn't
appear to have made much difference. Are there a set of values for
kernel parameters that would be advisable to make for a mail server?
Here is what I currently have:
# sysctl -p
net.ipv4.ip_forward = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq = 0
kernel.core_uses_pid = 1
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
net.ipv4.ip_forward = 1
net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.conf.all.log_martians = 0
net.ipv4.conf.default.log_martians = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
vm.vfs_cache_pressure = 35
vm.nr_hugepages = 512
net.ipv4.tcp_max_syn_backlog = 2048
fs.aio-max-nr = 1048576
vm.dirty_background_ratio = 3
vm.dirty_ratio = 40
After making changes, do you have any recommendations on which tools
to use to monitor those changes and see how they perform?
I have noatime set in fstab in the guest for the /var partition, where
much of the spamassassin occurs.
I've included below my libvirt xml config for the guest and hoped
someone could make some recommendations on how to apply the cputune
and memtune parameters to my system.
<domain type='kvm'>
<name>mail02</name>
<uuid>ec4f3cf5-2f27-fb3e-72f6-3fa3176b13b6</uuid>
<memory>8388608</memory>
<currentMemory>8388608</currentMemory>
<vcpu>8</vcpu>
<os>
<type arch='x86_64' machine='pc-0.14'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/bin/qemu-kvm</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/var/lib/libvirt/images/mail02.img'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
function='0x0'/>
</disk>
<disk type='block' device='cdrom'>
<driver name='qemu' type='raw'/>
<target dev='hdc' bus='ide'/>
<readonly/>
<address type='drive' controller='0' bus='1'
unit='0'/>
</disk>
<controller type='ide' index='0'>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x01'
function='0x1'/>
</controller>
<interface type='bridge'>
<mac address='52:54:00:67:2c:4c'/>
<source bridge='br0'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x03'
function='0x0'/>
</interface>
<serial type='pty'>
<target port='0'/>
</serial>
<console type='pty'>
<target type='serial' port='0'/>
</console>
<input type='mouse' bus='ps2'/>
<graphics type='vnc' port='-1' autoport='yes'/>
<video>
<model type='cirrus' vram='9216' heads='1'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x02'
function='0x0'/>
</video>
<memballoon model='virtio'>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x06'
function='0x0'/>
</memballoon>
</devices>
</domain>
Thanks,
Alex
1:41 p.m.
On Wed, Oct 05, 2011 at 02:28:30PM -0400, Alex wrote:
Load on the server is regularly above 20, yet the processors
generally are idle and the host is still responsive.
That's completely normal for an email server running spamassassin,
in my experience, and has nothing to do with libvirt. IME, the
issue is DNS lookups, which spamassassin and the RBLs it uses make
*heavy* use of. Run a caching DNS on localhost with fairly
agressive caching (i.e. go ahead and have it ignore TTLs and keep
everything for at least 5 minutes) and I expect that you'll find
that problem being rapidly resolved.
-Robin
3:08 p.m.
Hi,
> Load on the server is regularly above 20, yet the processors
> generally are idle and the host is still responsive.
That's completely normal for an email server running spamassassin,
in my experience, and has nothing to do with libvirt. IME, the
issue is DNS lookups, which spamassassin and the RBLs it uses make
*heavy* use of. Run a caching DNS on localhost with fairly
agressive caching (i.e. go ahead and have it ignore TTLs and keep
everything for at least 5 minutes) and I expect that you'll find
that problem being rapidly resolved.
Thanks for your help, but as much as I'd like it to be a simple DNS
issue, I really don't think that's the case. I have a caching
nameserver running, and while there sure is a lot of DNS traffic, it's
got to be more than that.
This mail server does manage a lot of mail per day, but not enough to
even consume the 8GB I've allocated, and the "mailq" command typically
takes a few seconds to respond, even when there's only a few messages
in the queue.
iotop may report as much as 2M/s on the host, with an average of about
400-600K/s. Does that seem like a lot? I can write like 80MB/s at
least using dd to test.
My configuration does not use any of the optional CPU or memory
parameters from libvirt, so I'm pretty sure there is something more
that can be done to improve performance, but I just don't know how.
Thanks for any ideas.
Alex
11:07 a.m.
On 10/6/11, Alex <mysqlstudent(a)gmail.com> wrote:
This mail server does manage a lot of mail per day, but not enough
to
even consume the 8GB I've allocated, and the "mailq" command typically
takes a few seconds to respond, even when there's only a few messages
in the queue.
iotop may report as much as 2M/s on the host, with an average of about
400-600K/s. Does that seem like a lot? I can write like 80MB/s at
least using dd to test.
I had similar problems previously. The crux in my case is the number
of IOPS possible. 100K of 2KB file writes is still 2MB/s but requires
a lot more IO overheads than 1 single 2MB file.
Recommendations that I was given which stopped the system from locking
up included
1. use ionice on the mail process
2. change the IO scheduler/elevator from the default CFQ
3. switch from file-based virtual drives to raw disk devices
4. mount filesystems with noatime
Also, are you using RAID 5?
11:16 a.m.
Hi,
> This mail server does manage a lot of mail per day, but not
enough to
> even consume the 8GB I've allocated, and the "mailq" command typically
> takes a few seconds to respond, even when there's only a few messages
> in the queue.
>
> iotop may report as much as 2M/s on the host, with an average of about
> 400-600K/s. Does that seem like a lot? I can write like 80MB/s at
> least using dd to test.
I had similar problems previously. The crux in my case is the number
of IOPS possible. 100K of 2KB file writes is still 2MB/s but requires
a lot more IO overheads than 1 single 2MB file.
Recommendations that I was given which stopped the system from locking
up included
1. use ionice on the mail process
2. change the IO scheduler/elevator from the default CFQ
3. switch from file-based virtual drives to raw disk devices
4. mount filesystems with noatime
Also, are you using RAID 5?
The only thing I haven't done from above is to use ionice on mail
processes. I'm using RAID5 across three 1TB SATA3 disks, I'm using
deadline scheduler, the /var partition is mounted noatime, and the
disk is mounted raw:
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/var/lib/libvirt/images/mail02.img'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
function='0x0'/>
How do I configure BIND to ignore TTLs and keep everything for five
minutes, as suggested?
Thanks,
Alex
4:34 a.m.
On 10/7/11, Alex <mysqlstudent(a)gmail.com> wrote:
The only thing I haven't done from above is to use ionice on
mail
processes. I'm using RAID5 across three 1TB SATA3 disks,
RAID 5 is another major bottleneck there. The commonly cited write
penalty for RAID 5 appears to be 4 IOPS, while RAID 1/10 is 2 IOPS.
Due to the typical load on an email server with more writes than read,
this become rather punishing.
So you might see a major improvement simply by adding another 1TB and
going for RAID 10.
Personally because of that, as well as the headache of recovering from
a RAID 5 disaster, I've stopped using RAID 5 especially since the cost
of drives are really cheap.
I'm using
deadline scheduler, the /var partition is mounted noatime, and the
disk is mounted raw:
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/var/lib/libvirt/images/mail02.img'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
function='0x0'/>
I meant raw disk devices rather than files e.g.
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
<target dev='vdb' bus='virtio'/>
</disk>
This eliminates one layer of filesystem overheads.
How do I configure BIND to ignore TTLs and keep everything for five
minutes, as suggested?
I'm not too sure about this sorry.
2:26 p.m.
Hi,
> The only thing I haven't done from above is to use ionice on
mail
> processes. I'm using RAID5 across three 1TB SATA3 disks,
RAID 5 is another major bottleneck there. The commonly cited write
penalty for RAID 5 appears to be 4 IOPS, while RAID 1/10 is 2 IOPS.
Due to the typical load on an email server with more writes than read,
this become rather punishing.
So you might see a major improvement simply by adding another 1TB and
going for RAID 10.
I thought RAID10 still involved RAID1 on all disks, so really the only
improvement would be the lack of the parity write, correct? The
wikipedia entry seems to indicate it's not all that much faster:
http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10
Am I just expecting more from kvm/qemu than is realistic at this
point? Are there no high-volume mail servers that use libvirt?
> <disk type='file' device='disk'>
> <driver name='qemu' type='raw'/>
> <source file='/var/lib/libvirt/images/mail02.img'/>
> <target dev='vda' bus='virtio'/>
> <address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
> function='0x0'/>
I meant raw disk devices rather than files e.g.
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
<target dev='vdb' bus='virtio'/>
</disk>
This eliminates one layer of filesystem overheads.
Can this type change be done without modifying the image, or must some
conversion be done prior to making this change?
I also found this cool doc on monitoring and improving performance:
http://www.ufsdump.org/papers/io-tuning.pdf
Thanks again,
Alex
9:20 p.m.
On Sun, Oct 09, 2011 at 03:26:52PM -0400, Alex wrote:
>> <disk type='file' device='disk'>
>> <driver name='qemu' type='raw'/>
>> <source file='/var/lib/libvirt/images/mail02.img'/>
>> <target dev='vda' bus='virtio'/>
>> <address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
>> function='0x0'/>
>
> I meant raw disk devices rather than files e.g.
> <disk type='block' device='disk'>
> <driver name='qemu' type='raw' cache='none'/>
> <source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
> <target dev='vdb' bus='virtio'/>
> </disk>
>
> This eliminates one layer of filesystem overheads.
Can this type change be done without modifying the image, or must
some conversion be done prior to making this change?
You can do that at any time; it just requires a reboot. You really
want caching off; see
http://publib.boulder.ibm.com/infocenter/lnxinfo/v3r0m0/index.jsp?topic=%...
-Robin
2:07 a.m.
On 10/10/11, Alex <mysqlstudent(a)gmail.com> wrote:
I thought RAID10 still involved RAID1 on all disks, so really the
only
improvement would be the lack of the parity write, correct? The
wikipedia entry seems to indicate it's not all that much faster:
Parity write and parity calculations. For a RAID 1 or RAID 10 setup,
you just write the same data to 2 disks. But for RAID 5, you need to
read, verify parity, calculate new parity, then write.
In terms of raw sequential bandwidth, the two don't differ that much
but it's the random IOPS that's the problem.
You can check out this post, it's meant for an Exchange 2007 server
but the calculations there clearly demonstrate the difference between
RAID 1/10 and RAID 5, it also assumes a 50/50 mix.
http://www.mmcug.org/blogs/Lists/Posts/Post.aspx?ID=16
There are also plenty of other tests and articles done to compare RAID
10 and RAID 5.
4:52 p.m.
Hi,
> I'm using
> deadline scheduler, the /var partition is mounted noatime, and the
> disk is mounted raw:
>
> <disk type='file' device='disk'>
> <driver name='qemu' type='raw'/>
> <source file='/var/lib/libvirt/images/mail02.img'/>
> <target dev='vda' bus='virtio'/>
> <address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
> function='0x0'/>
I meant raw disk devices rather than files e.g.
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
<target dev='vdb' bus='virtio'/>
</disk>
I made this change by editing the xml, restarting libvirtd, then using
virsh to define the xml file and received this message:
virsh # define /etc/libvirt/qemu/bwimail02.xml
error: Failed to define domain from /etc/libvirt/qemu/bwimail02.xml
error: missing source information for device vda
Have I done something wrong, or am I missing something?
Thanks for the other notes. I'm still trying to digest it all, but
continuing to make progress.
Thanks,
Alex
5:09 p.m.
On Mon, Oct 10, 2011 at 05:52:28PM -0400, Alex wrote:
Hi,
>> I'm using
>> deadline scheduler, the /var partition is mounted noatime, and the
>> disk is mounted raw:
>>
>> <disk type='file' device='disk'>
>> <driver name='qemu' type='raw'/>
>> <source file='/var/lib/libvirt/images/mail02.img'/>
>> <target dev='vda' bus='virtio'/>
>> <address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
>> function='0x0'/>
>
> I meant raw disk devices rather than files e.g.
> <disk type='block' device='disk'>
> <driver name='qemu' type='raw' cache='none'/>
> <source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
> <target dev='vdb' bus='virtio'/>
> </disk>
I made this change by editing the xml, restarting libvirtd, then using
virsh to define the xml file and received this message:
virsh # define /etc/libvirt/qemu/bwimail02.xml
error: Failed to define domain from /etc/libvirt/qemu/bwimail02.xml
error: missing source information for device vda
Have I done something wrong, or am I missing something?
You'll need to show us the xml file.
-Robin
5:13 p.m.
On 10/10/2011 03:52 PM, Alex wrote:
I made this change by editing the xml, restarting libvirtd, then
using
virsh to define the xml file and received this message:
virsh # define /etc/libvirt/qemu/bwimail02.xml
error: Failed to define domain from /etc/libvirt/qemu/bwimail02.xml
error: missing source information for device vda
Have I done something wrong, or am I missing something?
Yes, you goofed by directly editing /etc/libvirt. By doing that, you
are going behind libvirt's back - if your edits happen to work, then a
libvirtd restart will use them, but if you introduce a typo or other
problem, then it is your fault that libvirt can't get things to work.
If you had instead gone through the libvirt API (such as by using 'virsh
edit bwimail02'), then libvirt would do some sanity checking up front
and refuse to install your changes unless they were safe.
That said, your typo:
<source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
is that you used <source dev=/> instead of <source file=/>. Even if the
source is a raw block device on the host, you still call it out using
file= in the xml.
--
Eric Blake eblake(a)redhat.com +1-801-349-2682
Libvirt virtualization library http://libvirt.org
3:04 a.m.
New subject: [libvirt-users] Re: Performance tuning questions for mail server
The 10/10/11, Eric Blake wrote:
On 10/10/2011 03:52 PM, Alex wrote:
>I made this change by editing the xml, restarting libvirtd, then using
>virsh to define the xml file and received this message:
<...>
>Have I done something wrong, or am I missing something?
Yes, you goofed by directly editing /etc/libvirt. By doing that,
you are going behind libvirt's back - if your edits happen to work,
then a libvirtd restart will use them, but if you introduce a typo
or other problem, then it is your fault that libvirt can't get
things to work. If you had instead gone through the libvirt API
(such as by using 'virsh edit bwimail02'), then libvirt would do
some sanity checking up front and refuse to install your changes
unless they were safe.
Which is comunterintuitive, IMHO. Admins are used to edit configuration
files in /etc because most software are designed this way.
Files not designed to be edited may stand in /var. At least, current
files in /etc could have a header with comments from preventing manual
edition and tips on how to deal to change configuration. ,-p
--
Nicolas Sebrecht
6:44 a.m.
On 10/11/2011 02:04 AM, Nicolas Sebrecht wrote:
> Yes, you goofed by directly editing /etc/libvirt. By doing
that,
> you are going behind libvirt's back - if your edits happen to work,
> then a libvirtd restart will use them, but if you introduce a typo
> or other problem, then it is your fault that libvirt can't get
> things to work. If you had instead gone through the libvirt API
> (such as by using 'virsh edit bwimail02'), then libvirt would do
> some sanity checking up front and refuse to install your changes
> unless they were safe.
Which is comunterintuitive, IMHO. Admins are used to edit configuration
files in /etc because most software are designed this way.
Files not designed to be edited may stand in /var. At least, current
files in /etc could have a header with comments from preventing manual
edition and tips on how to deal to change configuration. ,-p
Which is exactly why newer libvirt sticks this header on such files
(here, from /etc/libvirt/qemu/domainname.xml):
<!--
WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
OVERWRITTEN AND LOST. Changes to this xml configuration should be made
using:
virsh edit domainname
or other application using the libvirt API.
-->
--
Eric Blake eblake(a)redhat.com +1-801-349-2682
Libvirt virtualization library http://libvirt.org
12:55 a.m.
On 10/11/11, Alex <mysqlstudent(a)gmail.com> wrote:
I made this change by editing the xml, restarting libvirtd, then
using
virsh to define the xml file and received this message:
virsh # define /etc/libvirt/qemu/bwimail02.xml
error: Failed to define domain from /etc/libvirt/qemu/bwimail02.xml
error: missing source information for device vda
Have I done something wrong, or am I missing something?
Will need to see your current XML to tell. But if you simply copied
and pasted my code, then it's definitely not going to work. For one
thing, you would need to have created a LVM volume named exactly the
same way I did.
If you simply changed the paremeters using your existing .img file as
the source, then it also won't work simply for obvious reasons.
1:29 a.m.
Hi,
<name>mail02</name <uuid>ec4f3cf5-2f27-fb3e-72f6-3fa3176b13b6</uuid <memory>4194304</memory
<currentMemory>4194304</currentMemory
<vcpu>8</vcpu <os <type arch='x86_64'
machine='pc-0.14'>hvm</type
<boot dev='hd'/ </os <features
<acpi/ <apic/ <pae/
</features <clock
offset='utc'/
<on_poweroff>destroy</on_poweroff
<on_reboot>restart</on_reboot
<on_crash>restart</on_crash
<devices
<emulator>/usr/bin/qemu-kvm</emulator
<disk type='file' device='disk'
<driver name='qemu' type='raw' cache='none'/ <source
file='/var/lib/libvirt/images/mail02.img'/
<target dev='vda' bus='virtio'/
<address type='pci' domain='0x0000' bus='0x00'
slot='0x05'
function='0x0'/ </disk <disk type='block' device='cdrom' <driver name='qemu' type='raw'/ <target dev='hdc' bus='ide'/ <readonly/
<address type='drive' controller='0' bus='1'
unit='0'/ </disk <controller type='ide' index='0' <address type='pci' domain='0x0000'
bus='0x00' slot='0x01'
function='0x1'/ </controller <interface type='bridge' <mac address='52:54:00:67:2c:4c'/ <source bridge='br0'/ <model type='virtio'/ <address type='pci' domain='0x0000'
bus='0x00' slot='0x03'
function='0x0'/ </interface <serial type='pty'
<target port='0'/ </serial <console type='pty'
<target type='serial' port='0'/
</console <input type='mouse'
bus='ps2'/ <graphics type='vnc'
port='-1' autoport='yes'/
<video <model
type='cirrus' vram='9216' heads='1'/
<address type='pci' domain='0x0000' bus='0x00'
slot='0x02'
function='0x0'/ </video <memballoon model='virtio' <address type='pci' domain='0x0000'
bus='0x00' slot='0x06'
function='0x0'/ </memballoon </devices
</domain
Thanks,
Alex
> I made this change by editing the xml, restarting libvirtd, then
using
> virsh to define the xml file and received this message:
> virsh # define /etc/libvirt/qemu/bwimail02.xml
> error: Failed to define domain from /etc/libvirt/qemu/bwimail02.xml
> error: missing source information for device vda
> Have I done something wrong, or am I missing something?
Will need to see your current XML to tell. But if you simply copied
and pasted my code, then it's definitely not going to work. For one
thing, you would need to have created a LVM volume named exactly the
same way I did.
If you simply changed the paremeters using your existing .img file as
the source, then it also won't work simply for obvious reasons.
Although I'm not very experienced with libvirt, I'd like to think I
have a reasonable grasp of the technology.
Perhaps I'm showing just how new at this I am, but what would be the
proper way using virsh to change the type to file instead of raw?
I've included my xml below, and would really appreciate any guidance
you may be able to offer. This is the pre-modified version.
One of the things I was working on was trying to get the host
processor spec to mirror that of the guest, but the guest had quite a
few deficiencies from the host, including less cache (4096kb vs
8192kb), and quite a few missing flags on the guest. How does that
impact performance?
This guest config was mostly generated by virt-manager on fedora15.
<domain type='kvm'
2:10 p.m.
Hi,
> iotop may report as much as 2M/s on the host, with an average of
about
> 400-600K/s. Does that seem like a lot? I can write like 80MB/s at
> least using dd to test.
I had similar problems previously. The crux in my case is the number
of IOPS possible. 100K of 2KB file writes is still 2MB/s but requires
a lot more IO overheads than 1 single 2MB file.
Can I also ask how you measured performance and the effect any changes
you made may have had on the system?
iotop seems very general. Perhaps sar? Ideas for graphing its output?
Thanks again,
Alex
4:41 a.m.
On 10/7/11, Alex <mysqlstudent(a)gmail.com> wrote:
Can I also ask how you measured performance and the effect any
changes
you made may have had on the system?
iotop seems very general. Perhaps sar? Ideas for graphing its output?
Well for that situation, people were screaming at me so I didn't
really measured things empirically. It was just throwing one possible
fix after another, while watching the system load iowait % go down
until things were smooth again.
Another key thing is having sufficient memory for the VM but I don't
think that's your problem since you have 8GB on it. Then again, it
would really depend on how much mails you are handling.
But if you have time for measurement, as well as can afford the
time/impact, you can try iozone which produces detailed stats and
includes graphing functionality IIRC.
The other tool I use is iostat.
Although I'm also thinking of writing a script that more closely mimic
the kind of loads on my typical server i.e. many small email files
written + some reads and random updates to a single large file (e.g.
log file, user db).
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