Jennifer Williams wrote:
Hi ,
I am having some problems when running in parallel. Although my jobs run
to completion I am getting some worrying domain decomposition statistics
in particular the average load imbalance and the performance loss due to
load imbalance see below:
Please report your GROMACS version number. If it's not the latest
(4.0.5), then you should probably update and see if it's a problem that
may have been fixed between those releases. You might also try it
without your freeze groups, especially if they dominate the system.
D O M A I N D E C O M P O S I T I O N S T A T I S T I C S
av. #atoms communicated per step for force: 2 x 1974.8
av. #atoms communicated per step for LINCS: 2 x 15.2
Average load imbalance: 500.0 %
Part of the total run time spent waiting due to load imbalance:
4246403072.0 %
Steps where the load balancing was limited by -rdd, -rcon and/or -dds:
X 9 %
NOTE: 4246403072.0 % performance was lost due to load imbalance
in the domain decomposition.
R E A L C Y C L E A N D T I M E A C C O U N T I N G
Computing: Nodes Number G-Cycles Seconds %
-----------------------------------------------------------------------
Write traj. 6 1001 18443320139.164 42130.9 100.0
Update 6 1000001 18442922984.491 42130.0 100.0
Rest 6 9223372036.855 21069.4 50.0
-----------------------------------------------------------------------
Total 6 18446422611.669 42138.0 100.0
-----------------------------------------------------------------------
NOTE: 305 % of the run time was spent communicating energies,
you might want to use the -nosum option of mdrun
Parallel run - timing based on wallclock.
NODE (s) Real (s) (%)
Time: 7023.000 7023.000 100.0
1h57:03
(Mnbf/s) (GFlops) (ns/day) (hour/ns)
Performance: 14.214 1.902 12.302 1.951
Finished mdrun on node 0 Wed Jul 29 23:47:18 2009
Below is my .mdp file: I am using the PME but not having much of a feel
for how to set the options under Spacing for the PME/PPPM FFT grid, I
left these as the default values. Could this be where the trouble lies?
My cut-off cannot be larger than 0.9 as my unit cell is only 18.2A in
one direction.
How do I choose values for PME/PPPM? Ie what kind of values to use for
nx, ny and nz ?
See manual section 3.17.5
I read that they should be divisible by npme to get the best
performance. Is npme the pme_order in the .mdp file? If not where do I
set this parameter?
No, -npme is a command line parameter to mdrun. Roughly speaking, things
that have a material effect on the physics are specified in the .mdp
file, and things that either require external file(names) to be supplied
or which only affect the implementation of the physics are specified on
the command line.
Mark
Much appreciated,
Jenny
; VARIOUS PREPROCESSING OPTIONS
; Preprocessor information: use cpp syntax.
; e.g.: -I/home/joe/doe -I/home/mary/hoe
include = -I../top
; e.g.: -DI_Want_Cookies -DMe_Too
define =
; RUN CONTROL PARAMETERS
integrator = md
; Start time and timestep in ps
tinit = 0
dt = 0.001
nsteps = 1000000
; For exact run continuation or redoing part of a run
; Part index is updated automatically on checkpointing (keeps files
separate)
simulation_part = 1
init_step = 0
; mode for center of mass motion removal
comm-mode = linear
; number of steps for center of mass motion removal
nstcomm = 1
; group(s) for center of mass motion removal
comm-grps =
; LANGEVIN DYNAMICS OPTIONS
; Friction coefficient (amu/ps) and random seed
bd-fric = 0
ld-seed = 1993
; ENERGY MINIMIZATION OPTIONS
; Force tolerance and initial step-size
emtol =
emstep =
; Max number of iterations in relax_shells
niter =
; Step size (ps^2) for minimization of flexible constraints
fcstep =
; Frequency of steepest descents steps when doing CG
nstcgsteep =
nbfgscorr =
; TEST PARTICLE INSERTION OPTIONS
rtpi =
; OUTPUT CONTROL OPTIONS
; Output frequency for coords (x), velocities (v) and forces (f)
nstxout = 1000
nstvout = 1000
nstfout = 0
; Output frequency for energies to log file and energy file
nstlog = 1000
nstenergy = 1000
; Output frequency and precision for xtc file
nstxtcout = 1000
xtc-precision = 1000
; This selects the subset of atoms for the xtc file. You can
; select multiple groups. By default all atoms will be written.
xtc-grps =
; Selection of energy groups
energygrps =
; NEIGHBORSEARCHING PARAMETERS
; nblist update frequency
nstlist =
; ns algorithm (simple or grid)
ns_type = grid
; Periodic boundary conditions: xyz, no, xy
pbc = xyz
periodic_molecules = yes
; nblist cut-off
rlist = 0.9
; OPTIONS FOR ELECTROSTATICS AND VDW
; Method for doing electrostatics
coulombtype = PME
rcoulomb-switch = 0
rcoulomb = 0.9
; Relative dielectric constant for the medium and the reaction field
epsilon_r =
epsilon_rf =
; Method for doing Van der Waals
vdw-type = Cut-off
; cut-off lengths
rvdw-switch = 0
rvdw = 0.9
; Apply long range dispersion corrections for Energy and Pressure
DispCorr = No
; Extension of the potential lookup tables beyond the cut-off
table-extension =
; Seperate tables between energy group pairs
energygrp_table =
; Spacing for the PME/PPPM FFT grid
fourierspacing = 0.12
; FFT grid size, when a value is 0 fourierspacing will be used
fourier_nx = 0
fourier_ny = 0
fourier_nz = 0
; EWALD/PME/PPPM parameters
pme_order =
ewald_rtol = 1e-05
ewald_geometry = 3d
epsilon_surface = 0
optimize_fft = yes
; OPTIONS FOR WEAK COUPLING ALGORITHMS
; Temperature coupling
tcoupl = nose-hoover
; Groups to couple separately
tc-grps = System
; Time constant (ps) and reference temperature (K)
tau_t = 0.1
ref_t = 150
; Pressure coupling
Pcoupl = No
Pcoupltype =
; Time constant (ps), compressibility (1/bar) and reference P (bar)
tau-p =
compressibility =
ref-p =
; Scaling of reference coordinates, No, All or COM
refcoord_scaling = no
; Random seed for Andersen thermostat
andersen_seed =
; GENERATE VELOCITIES FOR STARTUP RUN
gen_vel = yes
gen_temp = 150
gen_seed = 173529
; OPTIONS FOR BONDS
constraints = none
; Type of constraint algorithm
constraint-algorithm = Lincs
; Do not constrain the start configuration
continuation = no
; Use successive overrelaxation to reduce the number of shake iterations
Shake-SOR = no
; Relative tolerance of shake
shake-tol = 0.0001
; Highest order in the expansion of the constraint coupling matrix
lincs-order = 4
; Number of iterations in the final step of LINCS. 1 is fine for
; normal simulations, but use 2 to conserve energy in NVE runs.
; For energy minimization with constraints it should be 4 to 8.
lincs-iter = 1
; Lincs will write a warning to the stderr if in one step a bond
; rotates over more degrees than
lincs-warnangle = 30
; Convert harmonic bonds to morse potentials
morse = no
; ENERGY GROUP EXCLUSIONS
; Pairs of energy groups for which all non-bonded interactions are excluded
energygrp_excl =
; WALLS
; Number of walls, type, atom types, densities and box-z scale factor
for Ewald
nwall = 0
wall_type = 9-3
wall_r_linpot = -1
wall_atomtype =
wall_density =
wall_ewald_zfac = 3
; Non-equilibrium MD stuff
acc-grps =
accelerate =
freezegrps = SI_O
freezedim = Y Y Y
cos-acceleration = 0
deform =
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