[CP2K:7406] Load balancing for H2O-inputs

[Martin Küttler]

Hi Iain,

thank you very much for that detailed answer! Since I also have some old 
traces that I am wondering about: Did the load balancing in 2.x releases 
work like it does in 3.0?

Martin

On Friday, February 5, 2016 at 11:05:55 AM UTC+1, IBethune wrote:
>
> Hi Martin, 
>
> The load balancing algorithm in the released versions of the code (3.0 or 
> earlier) can be quite memory-hungry so is turned off when running on >1024 
> MPI processes.  You can also override this by setting 
> FORCE_EVAL%DFT%MGRID%SKIP_LOAD_BALANCE_DISTRIBUTED [TRUE|FALSE].  The fact 
> that you see these routines in the timing report indicates that the load 
> balancer is running.  If you turn it off you will find marginally worse 
> performance.  For the H2O-xxx benchmarks, the atoms are essentially 
> distributed at uniform density throughout the cell, so the problem is 
> fairly well load balanced to start with.  If you were running something 
> like an isolated cluster or a slab/interface you would likely see more 
> effect from using the load balancer (or not). 
>
> Also, bear in mind that you will not get 100% load balance even when the 
> load balancer is turned on as it works within certain constraints depending 
> on the number of processors, the resulting decomposition of the realspace 
> grids, and the system geometry.  Also, the main bits of work which are 
> balanced by this algorithm are the collocation and integration of gaussian 
> products (calculate_rho_elec and integrate_v_rspace in the timing report). 
>  Other parts of the code e.g. dbcsr are not affected by the 
> load_balance_distributed scheme. 
>
> In CP2K 4.0 (development trunk), the load balancer is improved so it is 
> less memory intensive and is turned on by default regardless of the number 
> of MPI processes 
>
> Cheers 
>
> - Iain 
>
> -- 
>
> Iain Bethune 
> Project Manager, EPCC 
>
> Email: ibe... at epcc.ed.ac.uk <javascript:> 
> Twitter: @IainBethune @PrimeGrid @CP2Kproject 
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>
> > On 5 Feb 2016, at 09:57, Martin Küttler <marti... at gmail.com 
> <javascript:>> wrote: 
> > 
> > Hi, 
> >   
> > I'm using the H2O input files from cp2k/tests/QS/benchmark. In the 
> output I see some times for subroutines that look like they do load 
> balancing (e.g. load_balance_distributed, optimize_load_list, 
> get_current_loads,...), but I don't see an effect of load balancing. Is 
> there a load balancer that works for these inputs? If so, when does it kick 
> in, and can it be turned on/off? 
> >   
> > Thanks, 
> > Martin 
> > 
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