[Ns-bugs] [Bug 695] DcfManager::UpdateBackoff () uses slow HighPrecision::Div()

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=695





--- Comment #14 from Pavel Boyko <boyko at iitp.ru>  2009-11-24 10:01:36 EDT ---
  Mathieu,

  thank you for explanations about history of Time.

> I suspect that if you try to make 100 stations _interfere_, then, yes, you will
> run into interesting problems but mainly because the underlying interference
> PHY model is O(n2) and, 

  Yes, now I know this too. Typical profile of large scale wifi simulation I
see:

samples  %        image name               symbol name
2361908309 68.2932  mesh-sc                 
ns3::InterferenceHelper::GetEnergyDuration(double)
185529257  5.3645  mesh-sc                 
ns3::InterferenceHelper::CalculateNoiseInterferenceW(ns3::Ptr<ns3::InterferenceHelper::Event>,
std::vector<ns3::InterferenceHelper::NiChange,
std::allocator<ns3::InterferenceHelper::NiChange> >*) const
91399806  2.6428  mesh-sc                 
ns3::DcfManager::GetBackoffStartFor(ns3::DcfState*)
88964737  2.5724  mesh-sc                 
ns3::DcfManager::GetAccessGrantStart() const

> hopefully, you can easily fix this by using a different
> PHY model. 

  Do you have one? We will try to optimize interference model when we'll have
some time (= students). 

> Otherwise, I would be happy to help fix any optimization issue you
> have with the wifi models to make them useful to you.

  Thank you! We will definitely return to wifi runtime optimizations.

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