Subject: RE: CPU usage

From: "Ross Walker" <ross(at)rosswalker.co.uk>
Date: Tue, 8 Feb 2005 10:53:01 -0800

You can lock the processor affinity of a process under windows by running
task manager and right clicking on the process and selecting set affinity.
You will need to do this with Gaussian's master thread so that all sub
threads inherit this affinity.
 
Also, you should double check what you mean by 60% usage. Do you mean 60% of
one cpu or 60% of the total? The bar on the left in task manager is the
total cpu usage, while the graphs are individual cpu usage. So on a REAL
dual cpu machine running one process this bar would show 50% usage. My
understanding is that Gaussian under windows is single cpu so this is the
best you can hope for. In hyper threaded environments things are a lot more
complicated since you don't actually have two cpus, just two pipelines.
Hence the total cpu usage gauge can be deceptive...
 
Note, if you manually switch hyper threading off in the bios and still see
only 60% cpu utilisation then chances are the process is spending most of
its time waiting for memory or swap rather than doing computation. In this
case there is not much you can do as you are limited by the machine
architecture.
 
So, short answer. "On a hyper threaded machine don't worry about the cpu
usage bar it is deceptive.". Only on a real dual cpu machine or single cpu
machine is it accurate.
 
All the best
Ross

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From: Computational Chemistry List [mailto:chemistry-request(at)ccl.net] On
Behalf Of Steve Bowlus
Sent: 07 February 2005 19:09
To: Rodrigo Pontes; chemistry(at)ccl.net
Subject: CCL:CPU usage

I have observed the same behavior with another quantum code on a machine
with the same CPU/OS combination.  There was an earlier post to this list
asking about what seemed to be a similar problem with the Xeon HT. 
 
I tentatively interpret the behavior that the job is given 100% of one of
the HT execution streams, while the other stream is largely kept idle.  I
have not found a way to tune this behavior. If you look at ControlPanels
>AdministrativeTools >ComputerManagement >Processors, you will see there are
two CPUs shown.  These can be uninstalled, but I haven't tried uninstalling
one.  Presumably, all CPU resources would be concentrated in a single
execution stream, but I haven't found any documentation on this point.  I
also haven't found anything to suggest the second "CPU" can be
_re_installed.  
 
I haven't talked to Intel or HP (who built my machine), either of whom could
shed light on all these issues.  Seems a pity that information on such a
feature (or limitation) of HT technology would not be made readily
available.
 
sb

 -----Original Message-----
From: Computational Chemistry List [mailto:chemistry-request(at)ccl.net]On
Behalf Of Rodrigo Pontes
Sent: Monday, February 07, 2005 9:29 AM
To: chemistry(at)ccl.net
Subject: CCL:CPU usage

Dear Colleagues,
 
We are running Gaussian on a Windows XP/Pentiun-IV HT 3.2GHz machine. We
observed (in the Task manager / performance) that the CPU usage is only
around 60%. Have someone noticed the same problem? How could us set the
configuration to a 100% CPU usage?
 
Thanks in advance,
 
Rodrigo M. Pontes
Departemanto de Quimica
Universidade Estadual de Maringa
Brazil

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