Dear colleage,

for one analysis at a time you do not gain much from dual procs when using SPM and the conventional binary libraries, since they cannot split themselves into tiny "calculation packages" for parallel processing. I just looked up a post on the list that offered some tweaked binaries that apparently can split up spm processing, to take advantage of 2 procs:

http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0312&L=spm&P=R6876&I=-1

I did not find the time yet to try it out, I might try it later this year. When you have experience with it I would appreciate it to hear what you find.

With conventional SPM, you do get some advantage because 1 proc is completely free for image processing, and the other can do OS related jobs for your windowing system, but this gain is modest. How much you save here heavliy depends on the linux distro and windows manager you use (assuming you do use linux). Windows is not good at either multi proc or 64 bit (for the latter no ready MS OS even exists as of yet).

The real advantage (up to 100% faster) occurs when 2 users process data simultanously (each in a separate matlab instance) on the same machine as compared to a single user, since each one can use their own proc.

For exact numbers you should do some benchmarking, or have a look at: http://www.psychology.nottingham.ac.uk/staff/cr1/spm99.html

Good luck,

Bas

-------------------------------------------
Dr. S.F.W. Neggers
dept. of Psychonomics,Helmholtz Institute
Utrecht University
Heidelberglaan 2
3584 CS, Utrecht, room 17.09
the Netherlands
Tel: (+31) 30 253 4582 Fax: (+31) 30 534511
E-mail: [log in to unmask]
Web: http://www.fss.uu.nl/psn/pionier
--------------------------------------------
-----Original Message-----
From: khead [mailto:[log in to unmask]]
Sent: dinsdag 4 januari 2005 23:21
To: Neggers, S.F.W. (Bas)
Subject: Re: [SPM] single vs dual processor


At 02:02 PM 1/4/2005, you wrote:
Hi: I saw the below post on the SPM list and am curious as to exactly *how* 
much of an advantage you actually get from a dual operton system. We have a 
huge amount of work coming up and I was going to ask my boss if we could 
get a faster machine. Is the dual processor a good cost benefit for SPM 
(which is virtually all we do with our machine)? Currently to perform 
optimized VBM it takes about 20 minutes per file and I do upwards of 40 
files at a time. It sounds as if I could even break the job up it might be 
worth it in time savings. Thanks for any advice you can give me.

>Dear Carolyn, list,
>
>I can second Satra's post. We run analyses of multiple users 
>simultanuously on a dual proc 64 bit opteron system. Note that matlab jobs 
>itself cannot (yet) be divided over 2 procs. Still, a major advantage is 
>that when one user runs an analyses, the next user has almost as good a 
>performance, provided your license allows you to run multiple matlab 
>instances simultanuously. A second advantage I really appreciate is that 
>when you run an analysis, it consumes all the CPU power of 1 proc, and the 
>other does operating system related things, and you work as smoothly on 
>your system as when no job is currently running. With one proc working on 
>the system when an analyses is runnen is a nuisance.
>
>I also read on the list some time ago that there apparently are efforts 
>out there to make the compiled C routines (that do all the hard work for 
>SPM and matlab) multithreadable so that even with 1 job running you might 
>be able to use both processors. You would have to search the list for that.
>
>Good luck,
>
>Bas
>
>-------------------------------------------
>Dr. S.F.W. Neggers
>dept. of Psychonomics,Helmholtz Institute
>Utrecht University
>Heidelberglaan 2
>3584 CS, Utrecht, room 17.09
>the Netherlands
>Tel: (+31) 30 253 4582 Fax: (+31) 30 534511
>E-mail: [log in to unmask]
>Web: http://www.fss.uu.nl/psn/pionier
>--------------------------------------------
>
>-----Original Message-----
>From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]On
>Behalf Of Satrajit Ghosh
>Sent: dinsdag 4 januari 2005 18:28
>To: [log in to unmask]
>Subject: Re: [SPM] single vs dual processor
>
>
>We have been very happy with our dual processors, particularly because
>we get to do several things simultaneously. However, given the
>increasing size of data sets and memory bottlenecks that come with a
>32-bit machine, I would recommend purchasing a 64 bit processor with
>lots of memory. Matlab 7.1 has support for 64 bit machines.
>
>Satra
>
>--
>Satrajit Ghosh
>Postdoctoral Associate
>Speech Communications Group
>Research Lab of Electronics, MIT
>
>On Tue, 4 Jan 2005 11:42:42 +0000, Cinly Ooi <[log in to unmask]> wrote:
> > Volkmar Glauche wrote:
> >
> > > On Mon, 3 Jan 2005, Carolyn L. Fort wrote:
> > >
> > >> I'm purchasing a Linux workstation that will be devoted to fMRI
> > >> processing/analysis and we'll primarily be running SPM (though AFNI,
> > >> FSL and other packages will be loaded as well). I'm wondering whether
> > >> SPM performs better on a dual processor or if sufficient speed (between
> > >> 2.8 - 3.2 GB) on a single processor will suffice.
> > >
> > >
> > > Matlab (and therefore SPM) will not make explicit use of a 2nd processor,
> > > but it is recommended if you want to use the workstation interactively
> > > while an analysis is running.
> >
> > Having a High speed processor waiting for interactive command is a bit
> > of a waste. I would prefer to take the penalty of sluggish workstation
> > response by running two analysis process on dual processor.
> >
> > Alternative is to get a single processor and hyperthread it. But
> > analysis speed can be slower, assuming that Data access (Ethernet/Hard
> > Disk/Cache) is not a limitting factor. May be dual processors,
> > hyperthread to 4 processors is a better proposition (3 analysis + 1
> > workstation activity). Unfortunately you cannot hyperthread only one
> > processor in a dual processors config.
> >
> > Cinly
> >