false-sharing | 易学教程

OpenMP False Sharing

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I believe I am experiencing false sharing using OpenMP. Is there any way to identify it and fix it? My code is: https://github.com/wchan/libNN/blob/master/ResilientBackpropagation.hpp line 36. Using a 4 core CPU compared to the single threaded 1 core version yielded only 10% in additional performance. When using a NUMA 32 physical (64 virtual) CPU system, the CPU utilization is stuck at around 1.5 cores, I think this is a direct symptom of false sharing and unable to scale. I also tried running it with Intel VTune profiler, it stated most of the time is spent on the "f()" and "+=" functions. I

performance counter events associated with false sharing

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I am looking at the performance of OpenMP program, specifically cache and memory performance. I have found guidelines while back ago how to analyze performance with Vtune that mentioned which counters to watch out for. However now cannot seem to find the manual. If you know which manual I have in question or if you know the counters/events, please let me know. Also if you have other techniques for analyzing multithreaded memory performance, please share if you can Thanks Here is an article discussion this topic . The most common counters to examine are L2 cache misses and branch prediction

Tools to detect False Sharing in a C/C++ application

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问题 Are there any tools that detect and report False Sharing for applications written in C or C++? 回答1: Try Sheriff and Predator. Sheriff is at https://github.com/plasma-umass/sheriff, while Predator is at https://github.com/plasma-umass/Predator. Predator is a compiler-based approach that you have to recompile your program using a new LLVM compiler. It is the most exhaustive detection tool up to now. Sheriff is library but it can only detect false sharing if you are using pthreads library. 回答2:

Parallel Framework and avoiding false sharing

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问题 Recently, I had answered a question about optimizing a likely parallelizable method for generation every permutation of arbitrary base numbers. I posted an answer similar to the Parallelized, poor implementation code block list, and someone nearly immediately pointed this out: This is pretty much guaranteed to give you false sharing and will probably be many times slower. (credit to gjvdkamp) and they were right, it was death slow. That said, I researched the topic, and found some interesting

Parallel Framework and avoiding false sharing

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Recently, I had answered a question about optimizing a likely parallelizable method for generation every permutation of arbitrary base numbers. I posted an answer similar to the Parallelized, poor implementation code block list, and someone nearly immediately pointed this out: This is pretty much guaranteed to give you false sharing and will probably be many times slower. (credit to gjvdkamp ) and they were right, it was death slow. That said, I researched the topic, and found some interesting material and suggestions (archived MSDN magazine only, .NET Matters: False Sharing ) for combating it

Are cache-line-ping-pong and false sharing the same?

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问题 For my bachelor thesis I have to evaluate common problems on multicore systems. In some books I have read about false sharing and in other books about cache-line-ping-pong. The specific problems sound very familiar, so are these the same problems but given other names? Can someone give me names of books which discuss these topics in detail? (I already have literature from Darry Glove, Tanenbaum,...) 回答1: Summary: False sharing and cache-line ping-ponging are related but not the same thing.

False sharing and pthreads

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问题 I have the following task to demonstrate false sharing and wrote a simple program: #include <sys/times.h> #include <time.h> #include <stdio.h> #include <pthread.h> long long int tmsBegin1,tmsEnd1,tmsBegin2,tmsEnd2,tmsBegin3,tmsEnd3; int array[100]; void *heavy_loop(void *param) { int index = *((int*)param); int i; for (i = 0; i < 100000000; i++) array[index]+=3; } int main(int argc, char *argv[]) { int first_elem = 0; int bad_elem = 1; int good_elem = 32; long long time1; long long time2;