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Low CPU benchmark performance on PV VM
Hi Xen-community,

I am running a CPU benchmark tool (LINPACK) on a PV VM inside Xen 4.5.1 on
Ubuntu 15.10 x64 on a IBM x3550 M4 server. This tool should consume all
possible CPU cycles available. I allocate 4 vCPUs by defining this in the
Xen PV (test.cfg). However, only 1 core and 4 threads are used:

CPU frequency: 2.494 GHz
Number of CPUs: 1
Number of cores: 1
Number of threads: 4

This is what lscpu says inside this Xen PV VM:

Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 4
On-line CPU(s) list: 0-3
Thread(s) per core: 4
Core(s) per socket: 1
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 62
Model name: Intel(R) Xeon(R) CPU E5-2609 v2 @ 2.50GHz
Stepping: 4
CPU MHz: 2500.062
BogoMIPS: 5000.12
Hypervisor vendor: Xen
Virtualization type: full
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 10240K
NUMA node0 CPU(s): 0-3

A HVM VM DO get all possible cores allocated inside the virtual node (see
below). These nodes have significant better performance then the Xen PV
virtual node.

CPU frequency: 2.494 GHz
Number of CPUs: 1
Number of cores: 4
Number of threads: 4

This is the DomU Xen host machine lscpu:

lscpu

Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 8
On-line CPU(s) list: 0-7
Thread(s) per core: 1
Core(s) per socket: 4
Socket(s): 2
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 62
Model name: Intel(R) Xeon(R) CPU E5-2609 v2 @ 2.50GHz
Stepping: 4
CPU MHz: 2500.062
BogoMIPS: 5000.12
Hypervisor vendor: Xen
Virtualization type: none
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 10240K
NUMA node0 CPU(s): 0-7


Xen vCPU list:

xl vcpu-list

Domain-0 0 0 7 -b- 10.1 all / all
Domain-0 0 1 2 -b- 6.5 all / all
Domain-0 0 2 4 r-- 2.6 all / all
Domain-0 0 3 0 r-- 3.9 all / all
Domain-0 0 4 3 -b- 4.4 all / all
Domain-0 0 5 6 -b- 2.6 all / all
Domain-0 0 6 5 -b- 4.7 all / all
Domain-0 0 7 7 -b- 2.9 all / all
test 3 0 1 -b- 1.5 0-3 / all
test 3 1 0 -b- 1.8 0-3 / all
test 3 2 0 -b- 0.7 0-3 / all
test 3 3 2 -b- 0.6 0-3 / all

xen DomU PV VM config:

cat test.cfg

bootloader = '/usr/lib/xen-4.5/bin/pygrub'

vcpus = '4'
memory = '2048'
cpus = "0-3"


Is there any options to give the paravirtualized guest the host-cpu
topology? In other words, how do I get Xen to use more vCPU cores?

Thanks!


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