yade-users team mailing list archive

[Chareyre <question215540@xxxxxxxxxxxxxxxxxxxxx>]

Question #215540 on Yade changed:
https://answers.launchpad.net/yade/+question/215540

Chareyre posted a new comment:
Thanks.
You could actually plot everything on the same graph more easily if y-axis was cycles*Nparticles / time.

A conclusion from these results seems to be that parallelism gives a 3x speedup, obtained with 3-4 cores, and there is no 
point using more than 4 cores.
This is not really what I concluded from my recent tests, but again: different simulation => different conclusions.

A few things to keep in mind:
- The collider (contact detection) is the main non-parallel task.
- the collider takes a larger part of the total time for larger number of particles, and for more dynamic simulations
- BUT it takes less time if verletDist is increased, at the price of more virtual interactions

In my recent tests, the collider was taking about 1% of the total time
(*), then it did not matter if the collider is parallel or not. If the
collider takes more than that, then it can explain why you get the best
speed with 3-4 cores when I get it with 8 cores.

In "--performance", the collider's cost goes from 1.8% (5k bodies) to
55% (200k bodies). This is partly because, the stats there include the
cost of initializing the collider (cost of the first iteration in any
simulation). Including this cost is not really correct: since the number
of steps is varying as a function of Nparticles, the 1st iteration will
take proportionaly more time with more particles but this is only
because the total number of iterations is smaller, then the result can't
be extrapolated in the form of an average time per step.

In the end, there is a clear answer to your question: no, --performance
is not good at testing parallelism and/or hardware.

(*) This information is available in the "--performance" output, 2nd
line in the table below. If you are currently running tests, it would be
good to record such data as it gives a better understanding of how/why
speed is affected by the different factors.

Name                                                    Count                 Time            Rel. time
-------------------------------------------------------------------------------------------------------
ForceResetter                                     12000             369078us                0.39%      
InsertionSortCollider                               337            1713474us                1.80%      
InteractionLoop                                   12000           74036435us               77.56%      
NewtonIntegrator                                  12000           19331902us               20.25%      
TOTAL                                                             95450891us              100.00%      

25091

-- 
You received this question notification because you are a member of
yade-users, which is an answer contact for Yade.