[Chicago] Kickstarter Fund to get rid of the GIL

[Brian Herman]

Whoa massimo can you give a talk on that stuff?


Arigatou gozaimasu,
(Thank you very much)
Brian Herman

brianjherman.com
brianherman at acm.org








On Mon, Jul 25, 2011 at 9:09 AM, Massimo Di Pierro
<mdipierro at cs.depaul.edu>wrote:

> Probably the single largest community in US using BlueGene machines is the
> lattice QCD community (in fact it was designed in collaboration with the
> lattice QCD group at Columbia University). The typical data structure
> consists of a 4D array (called lattice) of a 4-vector of SU(3) matrices (3x3
> complex double precision) and a few other similar data structures that live
> on a site of the 4D lattice. A typical lattice has 96x64^3 sites for a total
> size of 96x64^3x4x9x2x8=14GB. The total memory usage is larger because of
> copies and other data structures. One of the 4D dimensions is stored locally
> the other 3D is distributed in parallel. Each iteration of the algorithm
> involved computing about ~2000 elementary floating point operations per
> lattice site and communicating the site structure (4x9x2x8bytes) to each of
> the 2^3 neighbor processors. The most efficient code can use up to 100-1000
> CPU with a 50-80% efficiency. So if one computing node stores 96 sites it
> needs to perform ~20
>  K FLOPs and 8 send and 8 recv for 96x4x9x2x8 bytes each. This type of
> computations are limited by latency more than bandwidth. Communication is
> always next neighbor (this is common for all algorithms that solve or are
> equivalent to solving differential equations numerically).
>
>
>
> On Jul 25, 2011, at 8:51 AM, sheila miguez wrote:
>
> > On Sun, Jul 24, 2011 at 11:51 AM, Alex Gaynor <alex.gaynor at gmail.com>
> wrote:
> >
> >> I'll live :)  Anyway, the point I was getting is not that a message
> passing
> >> system is not scalable, I've written code for Blue Gene/Ls so I know
> that
> >> message passing scales.  But rather that, for problems for which
> >> shared-memory concurrency is appropriate (read: the valid cases to
> complain
> >> about the GIL), message passing will not be, because of the
> >> marshal/unmarshal overhead (plus data size/locality ones).
> >> ALex
> >
> > Are jobs for Blue Gene where there would be fairly sizable data
> > packets a rare use case? I don't know a lot about the typical use
> > cases, and am curious. I'm guessing the common case would be where
> > they would do analysis on things that could be split out, but am
> > curious about the size of the chunks of information.
> >
> >
> >
> > --
> > sheila
> > _______________________________________________
> > Chicago mailing list
> > Chicago at python.org
> > http://mail.python.org/mailman/listinfo/chicago
>
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