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Also about Amdahl's law

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  Also about Amdahl's law aminer <aminer@toto.net> - 2013-10-10 12:34 -0700

#3901 — Also about Amdahl's law

I wrote:
 > Hello,
 >
 > I think i know what is my mistake: the serial part in
 > the Amdahl's law is not the critical section, you must not
 > confuse the two.


But, Amine,  how can you say that the serial part of the Amdahl's law is 
not
the critical section ?


In my example if you don't have context switches , and you have the same
number of threads than the number of cores, and the time inside the 
critical
section is constant and the time inside the parallel part is constant, 
so the Amdahl's law can predict the worst case contention scenario , 
that means when all the threads are contending for the same critical 
section, hence you can predict the worst case contention scenario by 
just  calculating the time inside the critical section and the time 
inside the parallel part and doing the Amdahl calculation, this will 
give you the
exact result for the worst case contention scenario, so as you have
noticed the serial part of the Amdahl equation is not only the critical 
section, it's the critical section with a context, so you have to take
into consideration also the context, that means the context of the worst 
case contention scenario.


Thank you,
Amine Moulay Ramdane.

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