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About my previous post

Ramine

12/6/2014 11:52:00 PM

Hello,


I have wrote in my previous post this:


"I have benchmarked the distribute reader-write lock of Dmitry Vyukov
and i have found that it is so expensive that it takes over 16 or 32
cores to make it scale as Seqlock with 4 cores"


You will say that in computer science we need proof of what i am
saying above..

Here is my proof by using the Amdahl's law:


The distributed reader-writer mutex using a rwlock of Dmitry Vyukov
don't eliminate the full memory barrier in the reader side of the RWLock
used by the distributed reader-writer mutex of Dmitry Vyukov, this full
memory barrier does take 350 CPU cycles on my quadcore Q6600 and i think
it takes around the same cycles on Intel i7, i have just done a parallel
program benchmark between Seqlock and the distributed reader-writer
mutex of Dmitry Vyukov using a rwlock on x86 and it gives on read-mostly
scenario 25 microseconds with Seqlock and it takes around 165
microseconds with the Dmitry Vykov distributed reader-writer mutex
using a rwlock, it takes 165 microseconds because it is using an
expensive call to GetCurrentProcessorNumber() of Windows and it is using
full memory fences on the reader side and it is using more code on the
reader side , but this GetCurrentProcessorNumber() and full memory
fences on the Dmitry Vyukov algorithm are part of the parallel part of
the Amdahl's law, so they will scale, but they are so expensive compared
to Seqlock that it takes 16 to 32 cores on small to medium reader
section size to make it scale as a Seqlock on 4 cores, cause look at the
165 microseconds compared to the 25 microseconds, there is a big
difference, this is my proof , so the distributed reader-writer mutex
using a rwlock is scalable but it is too much slow than Seqlock or RCU
on reader-mostly scenarios, this is why i have invented my scalable
distributed sequential lock that beats Seqlock and that is as fast and
as scalable as both Seqlock and RCU on read-mostly
scenarios.

You can download my scalable distributed sequential lock version 1.1 from:

https://sites.google.com/site/aminer68/scalable-distributed-seque...


Thank you,
Amien Moulay Ramdane.