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About Amdahl law

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  About Amdahl law Ramine <ramine@1.1> - 2014-11-15 15:36 -0800
    Re: About Amdahl law Ramine <ramine@1.1> - 2014-11-15 15:38 -0800

#2679 — About Amdahl law

Hello,


I think that the Amdahl law is very important, cause it permits
us to understand better multicore programming and distributed 
programming, for example when you are doing a parallel matrix 
multiplication, you have to move two doubles and you have also to 
multiply them, an the act to multiplying them inside your computers will 
tale around 8 clocks if we don't use SIMD instructions, and the act to 
move the two doubles from the memory to the CPU will take around 1 
clock, so the parallel matrix multiplication will not scale more than 8X 
and that's what the Amdahl lawsays, and that's because of contention on 
the memory bus that must serialize the accesses to the memomoy , for the 
concurrent hashtable that's the same , if the data on the corresponding 
keys of the hashtable are more bigger so the data moving from the memory 
to the CPU will take much more CPU clocks and this will make the serial 
part of the Amdahl equation bigger , so this will make the concurrent 
hashtable to scale less and less, and that's also the Amdahl equation 
that says that... for databases systems such us Oracle they don't scale 
well on multicore systems, cause they are memory bound, so this is why 
you have to scale them by distributing your database on many computers 
and this will make the memory system and hardisk system truly parallel 
for the read transations and this is much better and that's also the 
Amdahl equation who says that, so all in all the Amdahl equation is a 
good tool that that modifies our perception on parallel programming and 
that permit us to undertand better the inner side of parallel programming.



Thank you,
Amine Moulay Ramdane.

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#2680

On 11/15/2014 3:36 PM, Ramine wrote:
>
> Hello,
>
>
> I think that the Amdahl law is very important, cause it permits
> us to understand better multicore programming and distributed
> programming, for example when you are doing a parallel matrix
> multiplication, you have to move two doubles and you have also to
> multiply them, an the act to multiplying them inside your computers will
> tale around 8 clocks if we don't use SIMD instructions, and the act to

around 8 clocks on x86 computers i mean.


> move the two doubles from the memory to the CPU will take around 1
> clock, so the parallel matrix multiplication will not scale more than 8X
> and that's what the Amdahl lawsays, and that's because of contention on
> the memory bus that must serialize the accesses to the memomoy , for the
> concurrent hashtable that's the same , if the data on the corresponding
> keys of the hashtable are more bigger so the data moving from the memory
> to the CPU will take much more CPU clocks and this will make the serial
> part of the Amdahl equation bigger , so this will make the concurrent
> hashtable to scale less and less, and that's also the Amdahl equation
> that says that... for databases systems such us Oracle they don't scale
> well on multicore systems, cause they are memory bound, so this is why
> you have to scale them by distributing your database on many computers
> and this will make the memory system and hardisk system truly parallel
> for the read transations and this is much better and that's also the
> Amdahl equation who says that, so all in all the Amdahl equation is a
> good tool that that modifies our perception on parallel programming and
> that permit us to undertand better the inner side of parallel programming.
>
>
>
> Thank you,
> Amine Moulay Ramdane.
>
>
>
>
>
>
>

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