[Beowulf] Feedback on large pages in Linux
toon at moene.indiv.nluug.nl
Mon Jul 17 15:20:25 EDT 2006
Valerie Henson wrote:
> Hello all,
> We are doing some work on large page support in Linux.
Yes, Yes, YES !!!
> Please reply directly to me, unless you have something to share with
> the whole list. Thanks!
Arggghhhh - you can't be serious.
> 1. What does your organization do?
My day time job (i.e., when I'm *not* working on GNU Fortran) at the
Dutch Weather Service entails improving our Limited Area Numerical
Weather Forecasting Model - hirlam.org).
> 2. What does your application do?
Forecasts the weather up to 48 hours in advance over the Atlantic +
Europe (at least, that's the default configuration).
> 3. How are large pages useful to you?
We use lots and lots of memory every time step in the model. Our
soon-to-be operational model uses ~ 1 Gbyte of memory per (~100) MPI
node every time step. There are 720 time steps (48 hours * 15 time
steps of 4 minutes real time per hour) during the 40 minute integration.
The job maximum time of 40 minutes is determined by our delivery dead
> 4. What is your experience with the Linux hugetlbfs implementation of
> large page support?
Haven't tried it yet. However, our experience on Solaris 9 (which
supports 4 Mbyte pages down to the compilation/link unit) is very
positive (this is on UltraSPARC III hardware).
> 5. Does Linux's large page support affect your decision whether or not
> to use Linux? If so, how?
Nope. We bought a Linux solution because hw+sw+other stuff was better
this way (SGI Altix).
> 6. What would make large page support in Linux better for your application?
Duh. Fewer TLB cache reloads.
Toon Moene - e-mail: toon at moene.indiv.nluug.nl - phone: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
A maintainer of GNU Fortran 95: http://gcc.gnu.org/fortran/
Gfortran At Work: http://mysite.verizon.net/serveall/moene.pdf
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