A QCD Grid: 5 Easy Pieces?

Richard KenwayUniversity of Edinburgh

Aug 2001 A QCD Grid: 5 Easy Pieces 2

the problem of quark confinement

• quarks come in six flavours • quarks are confined by the strong force (QCD) into bound states called hadrons

• we cannot directly measure the decay of one quark flavour into another– which may conceal clues to why matter dominates antimatter

• we need reliable simulations of the strong forces between the quarks in a hadron– to infer quark properties from hadron properties

Aug 2001 A QCD Grid: 5 Easy Pieces 3

lattice QCD• quantum mechanics + special relativity

– probabilities from averaging over many realisations– treat space and time on an equal footing hypercubic lattice

• performance number of processors

• lattice spacing must be extrapolated to zero keeping the box large enough– halving the lattice spacing

500 times more computer powera

L

• need c. 1000 teraflops years• QCDOC

– UK-US project– ASIC = PowerPC + 1 Gflops

FPU + 4 MB + 12 links– 5 Tflops / $1 per sustained

Mflops by end 2002– SciDAC funding for software

Aug 2001 A QCD Grid: 5 Easy Pieces 4

why build a QCD grid?

• the computational problem is too big for current computers– configuration generation is tightly coupled a few petaflops

machines, not metacomputing (yet)– post-processing is highly diverse and distributed

• it involves multinational collaborations – (overlapping) virtual organisations are well established and growing

• many terabytes of data should be federated– validity + security are essential, so data provenance is a vital issue

• extensive software exists and should be more widely exploited– must be correct, portable and efficient

QCDconfigurations

2

experiment

ubV

Aug 2001 A QCD Grid: 5 Easy Pieces 5

5 easy pieces(?)

1 data provenance• label configurations by physics parameters and history• planning to write data in XML format

2 data grid• federate global data with open + restricted access via physics

parameters• have translation codes: UKQCD Columbia MILC NERSC• planning data mirroring/caching across TByte RAID disk farms at

Glasgow, Edinburgh, Liverpool and Swansea• possibly extending to US and Germany

3 application code library• validate and maintain an open-source + restricted code base• UKQCD + Columbia are building a CVS repository• other US groups will contribute/exploit open-source codes

(SciDAC)

UKQCD objective: grid functionality, conforming to standards (eg GLOBUS, SRB) by exploiting leverage with other projects

Aug 2001 A QCD Grid: 5 Easy Pieces 6

5 easy pieces(?)4 QCD portal

• provide a high-level interface to codes, data and machines• considering a web form to write job scripts, construct I/O files,

submit and monitor jobs, and archive data• also to construct data analysis codes from library routines

5 computation grid• controlled access to global computers + charging mechanism• computational steering for unexplored parameter regions• a long way off!• farming post-processing jobs across UKQCD sites is a feasible

starting point

a QCD grid requires similar functionality to other grids (eg LHC, virtual observatory) but is on a more manageable scale and is

low riskinsufficient human resources are available to UKQCD today, but

the opportunity exists