Groups > comp.programming.threads > #2687

W have to be smart

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From	Ramine <ramine@1.1>
Newsgroups	comp.programming.threads
Subject	W have to be smart
Date	Tue, 18 Nov 2014 18:41:39 -0800
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Hello,

I have just read the following PhD paper about NUMA Cohort locks...

http://dspace.mit.edu/handle/1721.1/72670

and i have read also the following Master research paper about NUMA 
cohort locks...


https://cs.brown.edu/research/pubs/theses/masters/2012/ma.pdf


So we have to be smart please , so follow with me...

I have just read the above papers and i have completly understood there
algorithm, it uses local locks and a global lock and it look
like a distributed algorithm that tries to minimize at best the
inter-socket coherence traffic , so i have not had a problem to 
understand it easily, but i have not been satisfied with those papers, 
why ? if you read carefully the PhD paper above you will notice that
there benchmarks are saying that the Lock cohort scales to about 6x
compared with a non-Numa Lock... and they have explained this 6x scaling 
by the fact that  there Lock cohort tries to minimize at best the 
inter-socket coherence traffic , but i am not convinced by there 
explanation, cause this 6x scaling comes instead from the fact that
there is parallelism inside the function that permit us to enter
the local locks first , this parallelism is around 6 CPU clocks or so 
and there is another serial part of the cache-line transfer in there 
other function of two integers tranfers from the L2 cache memory to the 
CPU that is around two clocks CPU and there is a serial part that spins 
for about 4 ms, so from the Amdahl's law this will scale to around 6x ,
so the scaling don't come from the fact that they are minimizing
at best the inter-socket cache coherence  traffic as they are saying, 
but from the Amdahl's law that says so as i have just explained it to 
you, so if you are transfering more data from the L2 cache to the CPU 
inside the critical section of the Lock cohort there benchmarks with a 
Lock cohort will scale much less than 6x, so if you have undertstood 
what i want to say to you , is that the lock cohort doesn't bring you 
much scalability if you are transfering more than 4 bytes from the L2 
cache to the CPU inside the critical section of the Lock cohort cause 
this will scale much less than 6x, so what i want to say is that the 
non-NUMA locks are still useful i think , and my scalable MLock can be 
used also in realtime systems, the NUMA lock cohort can not.

You can download my scalable MLock from


https://sites.google.com/site/aminer68/scalable-mlock

Thank you for your time.


Amine Moulay Ramdane.

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W have to be smart Ramine <ramine@1.1> - 2014-11-18 18:41 -0800
  Re: W have to be smart Ramine <ramine@1.1> - 2014-11-18 19:10 -0800
  Re: W have to be smart Ramine <ramine@1.1> - 2014-11-18 19:46 -0800
    Re: W have to be smart Ramine <ramine@1.1> - 2014-11-18 20:02 -0800

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