Re: [SLE] Doubt about SMP's and parallel jobs
From: Rikard Johnels (rikard.j_at_rikjoh.com)
Date: 09/15/05
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To: suse-linux-e@suse.com Date: Thu, 15 Sep 2005 09:35:07 +0200
On Wednesday 14 September 2005 18.56, Rikard Johnels wrote:
> On Wednesday 14 September 2005 17.05, Randall R Schulz wrote:
> > Chaitanya,
> >
> > On Wednesday 14 September 2005 07:49, Chaitanya Krishna A wrote:
> > > Hi,
> > >
> > > This could be a bit off the list, but still ...
> > >
> > > The output of uname -a of my machine is as below
> > > Linux achala 2.6.11.4-21.8-smp #1 SMP Tue Jul 19 12:42:37 UTC 2005
> > > i686 i686 i386 GNU/Linux, and I guess SMP stands for Shared Memory
> > > Processor. I have a two processors on my mother board.
> >
> > SMP: "Symmetric Multi-Processor"; "Symmetric" because all processors are
> > co-equal in their capabilities and ability to access shared resources
> > such as memory and I/O ports / devices.
> >
> > > I am doing my work in Molecular Dynamics simulations. So most of the
> > > time I would be doing a lot of number crunching. Now if start a job
> > > on my machine, does it automatically run using both the processors on
> > > my machine, or will I have to use a message passing library like MPI
> > > to use both the processors?
> >
> > Nothing truly automatically parallelizes. Depending on the language used
> > to implement the application, it can be more or less work to exploit
> > multi-processor hardware. E.g., if the application is written in Java
> > ad you're using the latest JVM from Sun, then at a minimum you get
> > parallelization of I/O and garbage collection (w.r.t. to the main
> > thread or threads that perform the work of your application).
> >
> > > I experimented with this some time back, I ran the same job with
> > > ./executable and also mpirun -n 2 ./executable on my machine (no
> > > clustering or anything). The second one gave maginally better results
> > > and top showed two processes running. Can someone explain what's
> > > happening?
> >
> > Clearly you're referring to some specific MPI system (probably
> > <http://www-unix.mcs.anl.gov/mpi/>?) of which I'm not aware, so I
> > cannot say definitively whether it can exploit your multiprocessor x86
> > system. Are you certain your application is written to use this MPI
> > software?
> >
> > Keep in mind that depending on the nature of the algorithms that
> > dominate the application in question the magnitude of any speed-up
> > possible _in principle_ varies. In practice, of course, one rarely sees
> > the full speed-up that is possible because of various overhead in the
> > software the provides the parallelism (your MPI system, e.g.).
> >
> > > Regards,
> > > Chaitanya.
> >
> > Randall Schulz
> >
> > --
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>
> I have found that running calculations and image processing and other CPU
> intensive tasks only benefits if the code is parallelized from the start.
> The one thing that DOES speed up is the overall response of the system.
> (The number crunching thread use one CPU and the system the other.)
> But if the code is written to utilize SMP, then it will be alot faster.
> An example was my Dual Celeron 433 MHz (god rest) which was alot more
> responsive under heavy load, processing images than the current Single CPU
> P3/733 MHz running the same setup/system.
> (GIMP isnt written to utilize SMP systems).
>
>
> --
> /Rikard
>
> ---------------------------------------------------------------
> Rikard Johnels email : rikard.j@rikjoh.com
> Web : http://www.rikjoh.com
> Mob : +46 (0)763 19 76 25
> PGP : 0x461CEE56
> ---------------------------------------------------------------
>
> --
> Check the headers for your unsubscription address
> For additional commands send e-mail to suse-linux-e-help@suse.com
> Also check the archives at http://lists.suse.com
> Please read the FAQs: suse-linux-e-faq@suse.com
Here is some pointers:
http://www.tldp.org/HOWTO/SMP-HOWTO.html (Linux specific)
http://csdl2.computer.org/persagen/DLAbsToc.jsp?resourcePath=/dl/proceedings/&toc=comp/proceedings/icppw/2005/2381/00/2381toc.xml&DOI=10.1109/ICPPW.2005.46
(generic paper)
--
/Rikard
---------------------------------------------------------------
Rikard Johnels email : rikard.j@rikjoh.com
Web : http://www.rikjoh.com
Mob : +46 (0)763 19 76 25
PGP : 0x461CEE56
---------------------------------------------------------------
--
Check the headers for your unsubscription address
For additional commands send e-mail to suse-linux-e-help@suse.com
Also check the archives at http://lists.suse.com
Please read the FAQs: suse-linux-e-faq@suse.com
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