Hello
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 solve.
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 (
https://github.com/akopytov/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
either.
Here is the info which I think that should be relevant for
the software versions in use. Feel free to ask for any additional
info.
[root@t7 ~]# xl info
host : t7
release : 4.9.215-36.el7.x86_64
version : #1 SMP Mon Mar 2 11:42:52 UTC 2020
machine : x86_64
nr_cpus : 8
max_cpu_id : 7
nr_nodes : 1
cores_per_socket : 4
threads_per_core : 1
cpu_mhz : 3000.122
hw_caps :
bfebfbff:000ce3bd:20100800:00000001:00000000:00000000:00000000:00000000
virt_caps : pv hvm
total_memory : 57343
free_memory : 53620
sharing_freed_memory : 0
sharing_used_memory : 0
outstanding_claims : 0
free_cpus : 0
xen_major : 4
xen_minor : 12
xen_extra : .2.39.g3536f8dc
xen_version : 4.12.2.39.g3536f8dc
xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p
hvm-3.0-x86_32 hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler : credit2
xen_pagesize : 4096
platform_params : virt_start=0xffff800000000000
xen_changeset :
xen_commandline : placeholder dom0_mem=1024M,max:1024M
cpuinfo com1=115200,8n1 console=com1,tty loglvl=all
guest_loglvl=all ucode=-1
cc_compiler : gcc (GCC) 4.8.5 20150623 (Red Hat
4.8.5-39)
cc_compile_by : mockbuild
cc_compile_domain : centos.org
cc_compile_date : Tue Apr 14 14:22:04 UTC 2020
build_id : 24148a191438467f26a9e16089205544a428f661
xend_config_format : 4
[root@t5 ~]# xl info
host : t5
release : 4.9.215-36.el6.x86_64
version : #1 SMP Mon Mar 2 10:30:40 UTC 2020
machine : x86_64
nr_cpus : 8
max_cpu_id : 7
nr_nodes : 1
cores_per_socket : 4
threads_per_core : 1
cpu_mhz : 2000
hw_caps :
b7ebfbff:0004e33d:20100800:00000001:00000000:00000000:00000000:00000000
virt_caps : hvm
total_memory : 12287
free_memory : 6955
sharing_freed_memory : 0
sharing_used_memory : 0
outstanding_claims : 0
free_cpus : 0
xen_major : 4
xen_minor : 8
xen_extra : .5.86.g8db85532
xen_version : 4.8.5.86.g8db85532
xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p
hvm-3.0-x86_32 hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler : credit
xen_pagesize : 4096
platform_params : virt_start=0xffff800000000000
xen_changeset :
xen_commandline : dom0_mem=1024M,max:1024M cpuinfo
com1=115200,8n1 console=com1,tty loglvl=all guest_loglvl=all
cc_compiler : gcc (GCC) 4.4.7 20120313 (Red Hat
4.4.7-23)
cc_compile_by : mockbuild
cc_compile_domain : centos.org
cc_compile_date : Thu Dec 12 14:34:48 UTC 2019
build_id : da34ae5b90c82137dcbc466cd66322381bc6fd21
xend_config_format : 4
Note: with all other kernels and xen versions that were
published for C6 during the last year, the performance was the
same, i.e. slow
The test VM is exactly the same, copied among servers:
[root@t7 ~]# cat /etc/xen/test7_1
builder = "hvm"
xen_platform_pci=1
name = "Test7"
memory = 2048
maxmem = 4096
vcpus = 2
vif = [ "mac=00:14:5e:d9:df:50,bridge=xenbr0,model=e1000" ]
disk = [ "file:/var/lib/xen/images/test7_1,xvda,w" ]
sdl = 0
vnc = 1
bootloader = 'xenpvnetboot'
#bootloader_args = ['--location',
'http://internal.x.y/mrepo/centos7-x86_64/disc1/']
_on_poweroff_ = 'destroy'
on_reboot = 'restart'
on_crash = 'restart'
#boot="nd"
boot="d"
pae=1
acpi=1
apic=1
tsc_mode=0
Notes:
- the lines past "boot" in the config do not make any difference
either, they were added during the last week's tests.
- I've tested with 1, 2, 4 and 8 VCPUs . There is no diff for the
real life apps.
Frankly in this moment I have no idea what else to change or test so .. please help.
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