RE: [Xen-users] Assign multiple cpu's to a single vcpu

["Artur Linhart - Linux communication" <AL.LINUX@xxxxxxxxxxx>]

Hello,

        There are following options as far as I know - but You maybe know it
already, it is commonly known:
A. Flag vcpus:
vcpus=N # N .. number of virtual processors
B. flag cpus:
#cpus = "" # leave to Xen to pick
#cpus = "0" # all vcpus run on CPU0
#cpus = "0-3,5,^1" # run on cpus 0,2,3,5

I have installed in the last week two DomUs with the MySQL for tests, so
maybe I could test Your problems on my instances if I can reproduce the
problems - but I am not very skilled in MySQL, so can you help me - how did
You figure out the MySQL daemon is not using more than 1 vcpu? The only
statement/diagnostics inside of MySQL which I found is something like

show engine InnoDB status;

But there is written nothing about the CPUs...

I do not think one thread could run on more CPUs - but at least there are
more threads running if You run MySQL... I do not understand what does it
mean if You write " MySQL did not support threading natively "... As far as
I know, nearly every DBMS supports the processing of the requests (at least
from multiple clients) in multiple threads - if all clients would run only
in 1 thread, the performance would be very very poor...

The poor performance of the DB can also be connected with the fact You use
the DOmU installed in a file, not on the block device, what causes a common
performance problems in the case of heavy R/W disk operations - what can be
the problem i the case of DB management systems.

What MySQL Version do You use?

        With best regards

                Archie

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Shem Valentine
Sent: Tuesday, August 21, 2007 9:17 AM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Assign multiple cpu's to a single vcpu

Hello list,

This is my first attempt at running Xen, and so far it has been
incredible.  However, I don't think it's going to work for the specific
application I was trying to use it for.

We have a web management system which uses a MySQL backend.  We have put
the MySQL server on a dual cpu motherboard with 2 dual-core XEON's with
hyperthreading.  I noticed that MySQL would only run on one core with a
total CPU usage of 25% (due to performance issues I had disabled
hyperthreading).  While searching forums and such about MySQL threading
a few people had mentioned going VMWARE because MySQL did not support
threading natively.  However I am a big fan open source and I like that
Xen was not a userspace virtualization so I gave it a try.

I've been running into the same problem with Xen.  I cannot get it to
use more than one core with MySQL.  What I am looking to do is have the
DomU have one vcpu and have Xen thread it's vcpu across all 8 physical
cpus.  I am naive in thinking this is possible with any virtualization?

When doing my research the User Manual seems to say that this is possible:
" Xen allows a domain's virtual CPU(s) to be associated with one or more
host CPUs. This can be used to allocate real resources among one or more
guests, or to make optimal use of processor resources when utilizing
dual-core, hyperthreading, or other advanced CPU technologies."

If this is possible, how would one configure it?

Thank you for your time,
-Shem Valentine

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