Re: very low performance of Xen guests

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On 15-06-2020 23:42, Manuel Wolfshant wrote:
On 6/15/20 2:46 PM, Stephen John Smoogen wrote:

On Sun, 14 Jun 2020 at 14:49, Manuel Wolfshant
<wolfy@xxxxxxxxxxxxxxxxxx> wrote:


For the past months I've been testing upgrading my Xen hosts
to CentOS 7 and I face an issue for which I need your help to

The testing machines are IBM blades, model H21 and H21XM.
Initial tests were performed on the H21 with 16 GB RAM; during the
last 6=7 weeks I've been using the H21XM with 64 GB. In all cases
the guests were fully updated CentOS 7 -- initially 7.6 ( most
recent at the time of the initial tests ), and respectively 7.8
for the tests performed during the last 2 months.  As host I used
initially CentOS 6 with latest kernel available in the centos virt
repo at the time of the tests and CentOS 7 with the latest kernel
as well. As xen versions I tested 4.8 and 4.12 ( xl info included
below ). The storage for the last tests is a Crucial MX500 but
results were similar when using traditional HDD.

My problem, in short, is that the guests are extremely slow.
For instance , in the most recent tests, a yum install kernel
takes cca 1 min on the host and 12-15 (!!!) minutes in the guest,
all time being spent in dracut regenerating the initramfs images.
I've done rough tests with the storage  ( via dd if=/dev/zero
of=a_test_file size bs=10M count=1000 ) and the speed was
comparable between the hosts and the guests. The version of the
kernel in use inside the guest also did not seem to make any
difference . OTOH, sysbench ( ) as well as p7zip benchmark
report for the guests a speed which is between 10% and 50% of the
host. Quite obviously, changing the elevator had no influence

Here is the info which I think that should be relevant for the
software versions in use. Feel free to ask for any additional

Is there a way to boot up a PV guest versus an HVM?

If I understood the docs correctly, newer xen does only PVHVM (
xen_platform_pci=1 activates that ) and HVM. But they say it's better
than PV. And I did verify, PVHVM is indeed enabled and active

You can also test running your Linux domUs as Xen PVH [1], which requires kernel 4.11 and Xen 4.10 as a minimum.


Adi Pircalabu
CentOS-virt mailing list

[Index of Archives]     [CentOS Users]     [Linux Media]     [Asterisk]     [DCCP]     [Netdev]     []     [Xfree86]     [Linux USB]

  Powered by Linux