Omer,
See my response following your initial post.
--------Original Message--------
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Omer Khalid
Sent: Monday, October 06, 2008 04:51
To: xen-users list
Subject: [Xen-users] VCPU and CPU Manipulation
Hi,
I have a dual core SMP machine ( in total 4 cores). I have been trying to set
restrict vcpu/cpus for my domU to one core/one vpcu but it have not fully
worked. As there are two commands "xm vcpu-set" and "xm vcpu-pin". By using
these commands, i have observed that the sequence in which they are used plays
a role. e.g. I have the following state in the beginning:
[root@lxb ~]# xm vcpu-list
Name ID VCPUs CPU State Time(s) CPU Affinity
==== == ===== ==== ==== ====== === =====
Domain-0 0 0 3 r-- 5593.4 any cpu
Domain-0 0 1 1 -b- 15361.9 any cpu
Domain-0 0 2 0 -b- 10137.5 any cpu
Domain-0 0 3 - --p 78.9 any cpu
test_lxb 20 0 2 -b- 21169.0 any cpu
What I want to achieve is that my domU (test_lxb) uses one VCPU pinned to one
CPU. In the above state, both my domU and dom0 are using VCPU 0 (which is
pinned to use either CPU 3 or 2.) After few "vcpu-set" and "vcpu-pin", I reach
the following stage where dom0 is pinned to CPU 3 and domU (test_lxb) is pinned
to CPU 2:
[root@lxb ~]# xm vcpu-list
Name ID VCPUs CPU State Time(s) CPU Affinity
Name ID VCPUs CPU State Time(s) CPU Affinity
==== == ===== ==== ==== ====== ========
Domain-0 0 0 3 r-- 5600.4 3
Domain-0 0 1 3 -b- 15372.5 3
Domain-0 0 2 3 -b- 10140.0 3
Domain-0 0 3 - --p 78.9 3
test_lxb 20 0 2 -b- 21169.5 2
But domU is still using VCPU 0 which is also used by my domU; now i would like
to restrict VCPU 0 to CPU 2 only for domU only...I am wondering how to achieve
this last mile?
Any ideas? Thanks for you help in advance!
Regards
--
Omer
-------------------------------------------------------
CERN -- European Organization for Nuclear
Research, IT Department, CH-1211,
Geneva 23, Switzerland
You have misinterpreted the meaning VCPU numbers. VCPU 0 is the first
virtual CPU for any domain, VCPU 1 is the second virtual CPU for any domain,
etcetera. Additional single VCPU domUs will have a VCPU 0 as well. Each VCPU
0 is actually a separate VCPU; they are all identified as CPU 0 to a different
domain, and the VCPU identification just tells you what the domU sees them as
(minus the V). CPU indicates which CPU/core a VCPU is currently using, and CPU
Affinity indicates which ones it is allowed to use. Furthermore, for
performance reasons, if you want Dom0 to only use one CPU/core, you should
assign it only one VCPU (which will be 0, so for what you are trying to do, you
probably ultimately want output more like this):
Name ID VCPU CPU State Time(s) CPU Affinity
Domain-0 0 0 0 r-- 5600.4 0
test_lxb 1 0 1 -b- 21169.5 1
test_abc 2 0 2 -b- 21169.5 2
test_def 3 0 3 -b- 21169.5 3
Obviously state and time will be variable. Additionally, which
core/cpu is used for which domain shouldn't matter much. Regarding getting to
this state, the number of VCPUs dom0 has initially (and which CPUs/cores they
use) is configurable (probably /etc/xen/xend-config). The same is true for
domUs. That said, see the example configs in /etc/xen for more info on how to
do this, but you should be able to cause each domU to start up with the
CPU/core you want it to use, and then you won't really need to use vcpu-set or
vcpu-pin. Finally, if I don't bring it up, someone else probably will, the
idea behind virtualization is to better use available processing power. With
that in mind, your domUs may not each need their own full CPU/core. (For
instance, I have a quad-core with four HVMs that have one vcpu each, where each
uses a separate core, and then my dom0 has four VCPUs, where each uses a
separate core; even this isn't by any means fully utilizing the hardware, but I
am more concerned with maintaining optimal performance of my HVMs). Good luck
with your project,
Dustin
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